Why do my two dogs fight at home, and how do I make peace between them?

You put the key in the lock and you can already hear the growling. When the door opens, your two dogs, who rubbed along happily for a year and a half, are locked together on the doormat. For a month now it has happened almost every time you come home. Or the story is a different one: you brought a puppy home, and the older dog lifts his lip whenever the puppy comes near you on the sofa. Everyone tells you it is jealousy. What we see on the training field is plainer and easier to work with: two dogs squabbling over the things they both value. Most of the time, you are at the top of that list.

Below is where the squabbles start, how to stop a fight without ending up in A&E yourself, and how to get a calm house back. It takes weeks, not days.

Why do two dogs who live together fight?

Two dogs sharing a home are negotiating all day long. Who goes out of the door first, who gets the spot next to you on the sofa, whose is the bone left on the rug, who sleeps by the radiator. Nearly all of it gets settled with a look, a shift of weight and the occasional sigh, without a sound you would hear from the kitchen. A fight happens when the negotiation has broken down, or when one of them has decided the other's signals no longer count.

To find out what is being negotiated in your house, keep a diary for a week of every tense moment, including the ones that ended without contact. Write down the time, the room, what object was nearby, who started it, who backed off and where you were. After seven days there is usually a pattern you had not spotted.

You are the prize

You stroke one dog and the other barges in between you. He nudges your hand away with his nose, climbs onto you. What people call jealousy is, in dogs, competition for your attention, and it is very real. The dog who shoved the other one aside and then got the fuss has learned that shoving works. Once it has worked often enough, the step after shoving is a bite.

The good spots and the food

The sofa, your bed, the soft basket, the bowl, the chew, the toy someone was playing with five minutes ago. A dog who growls with a bone in his mouth as the other walks past is guarding something that matters to him. Guarding is normal dog behaviour. Trouble starts when two dogs in the same house are guarding the same thing.

Age

The puppy the older dog put up with at five months turns, at 18 to 24 months, into an adult who no longer gives way. Dogs mature properly, including in how they handle other dogs, between eighteen months and three years, and that is when most fights break out between dogs who "used to get on perfectly". At the other end of life is the old dog in pain, who can no longer hold the place he held for years.

Two dogs of the same sex

In the cases described in the veterinary behaviour literature, the worst fights within one household are between two dogs of the same sex, and above all between two bitches close in age and size. We see the same thing. There are exceptions. Even so, if you have two bitches who have drawn blood, take the plan below very seriously.

Excitement that spills over

The doorbell goes, a dog passes the window, voices get raised in the kitchen. Arousal shoots up all at once, and the bite meant for the passer-by lands on whichever dog is standing closest. That is why so many fights happen at the front door, at the window and in the first thirty seconds after you walk in.

The warning that got punished out

A dog told off every time he growls stops growling. Next time he goes straight in. It is like taking the battery out of the smoke alarm because the beeping annoyed you.

Pain or illness in one of them, particularly the older dog, can turn the whole relationship upside down. More on that in the medical section further down.

Which mistakes make dog fights worse?

"Let them sort it out between themselves" sometimes works with three-month-old puppies. With two adults carrying four-centimetre canines, every fight makes the next one more likely and shortens the road from growl to bite. The dogs come away believing that fighting is how things get settled.

You still hear the advice in parks to "back the dominant dog": feed the stronger one first, let him through the door first, fuss him first, to "confirm the hierarchy" so the other one settles down. The wolf-pack theory behind it was withdrawn by the very scientist who put it forward, once he had studied wild wolves instead of unrelated wolves crammed into an enclosure. Pick a favourite and the other dog gets more frustrated, while the doorway stays exactly as it was.

Telling a dog off for growling takes away the only warning you get before a bite. The growl goes and the bite stays. A dog who growls is showing you where his limit is, which is exactly the spot to start working from.

Punishing both of them after the fight is another trap. You come out of the bathroom, find it already over and tell them both off. The dog who was attacked learns that the other dog's company brings a fight and a row from you, so next time he defends himself sooner and harder.

Putting your hands between them is the quickest way to A&E. Most of the bites people get in dog fights are accidental: a hand goes in next to two mouths that have just clamped onto something. Do not grab collars mid-fight.

Forced reconciliation, both dogs held on short leads, face to face, "so they make up", ends badly. A tight lead tells each dog that you are tense too, and a dog who cannot move away attacks.

How to get two dogs living calmly together again

There are five parts. The first two start today. The rest begin once you have had at least three days without a single incident.

1. Safety, from day one

• When you are out or cannot keep an eye on them, they are kept apart: different rooms, a baby gate, crates if they already know them. That rule stays until you have four weeks in a row with no tense moment in the diary.
• They eat in separate rooms with the door shut, and bowls are picked up straight after the meal. Bones, chews and the single water bowl in the corner either come off the floor or get doubled up.
• The sofa and the bed are off limits for both, for now. Each has his own bed, in different corners of the room.
• Prepare in advance for the flashpoints in the diary (the doorbell, you coming home, the window). One dog is already in another room before anyone rings. You walk in low-key, back turned, until they have calmed down.
• If there has been a bite that broke the skin, both wear basket muzzles when they are together. Spend a few days turning the muzzle into a game first: cheese fed through it, a few seconds wearing it, then longer.

2. How to break up a fight without getting bitten

However much you want to reach in, keep your hands out. Use a short, loud noise (a door slammed, a saucepan lid dropped on the tiles), a bucket of water, or something big pushed between them: a sofa cushion, a chair, a tray. If there are two of you, each grabs one dog by the back legs, lifts and pulls him backwards in an arc, like a wheelbarrow, and takes him straight into another room without turning him to face the other dog.

Then check both dogs with your hands through the coat, not just by eye. Dog bites look small on the skin and go deep underneath. After a fight with contact, they are fully separated for 48 hours, then you start again from step 1.

3. Less to compete for

Each dog gets ten minutes a day alone with you, door shut, while the other works on a chew in another room. When your attention is guaranteed every day, it is no longer scarce enough to fight over. The rest of the time, fuss comes in turns and in short doses. The dog who pushes in between you is calmly sent to his bed, and there you praise him and give him a tasty bit.

Double up on what they value: two water bowls in two rooms, two beds, two identical toys. The rules are the same for both and there is no favourite. Neither gets on the sofa, both wait at the door, both get their food after they have sat down.

Bring the arousal down across the whole house too: separate sniffy walks on a long line, less wrestling in the living room, the doorbell switched off for a month and visitors texting to say they have arrived.

4. Rebuilding, on lead

Start outdoors with parallel walks. Two people, two dogs, same street, same direction, five metres apart, both dogs with their noses in the grass. When both have walked relaxed for ten minutes, the next day the gap shrinks by a metre.

Indoors, one dog lies on his mat practising a stay with you, with praise and tasty bits, while the other does the same three metres away with the second person. Then you swap. The moment you are waiting for is when one dog looks at the other and then turns back to you. That is when you light up, tell him how brilliant he is and give him the best bit in the bag.

After two or three weeks of parallel walks with no incident, give them short spells together indoors with the leads trailing on the floor, so you can step in without a hand anywhere near a mouth. Start with ten minutes and split them up before they get tired and scratchy. If the diary stays clean, add five minutes a day.

5. The first week

Could there be a medical cause?

When two dogs who have got on for years suddenly start fighting, the cause is often in one dog's body:

• the old dog with arthritis or toothache growls when the other jumps up next to him on the sofa, because it hurts and he can no longer get out of the way quickly;
• the dog whose sight or hearing is going gets caught by surprise and reacts as if he were being attacked;
• in dogs over ten, an ageing brain (cognitive decline) changes how they recognise the dog they live with;
• in entire bitches, seasons and false pregnancies change the relationship for weeks;
• some hormonal imbalances and some long-standing pain make a dog shorter-tempered with no other visible sign.

Take both dogs for a check-up: the one who seems to be starting it and the one who has suddenly backed down. Tell your vet the date of the first incident and what changed at home in the month before.

What nose work does for two dogs who squabble

Nose work will not reconcile them, and it does not replace keeping them apart. What we see in training, with dogs from the same household who come one after the other, is that each gets 30 to 40 minutes alone with you and a hard job to do, and goes home tired in the right way. In the evening there is nothing left in the tank for guarding the sofa. At home, search games happen with the door shut. One dog hunts for bits of food around the room while the other waits his turn next door with a chew.

When to call in a behaviour professional

• there has been a bite that broke the skin, on a dog or a person;
• fights are getting more frequent or kicking off faster, without a growl first;
• one dog is hiding, has stopped eating or avoids the rooms the other dog is in;
• the fights happen right next to you or next to a child;
• two bitches have fought badly more than once; here, sometimes, the honest answer is permanent separation or a new home for one of them, and a professional helps you make that call with a clear head before a serious injury;
• you have stuck to the plan for four weeks and the diary shows no improvement.

The assessment starts from your diary and from what happens in your house, with each dog seen in turn. Afterwards you will know whether you need a behaviour programme or just a few rules kept more strictly.