My dog bit a new dog. How to introduce aggressive dogs safely?

It sounds like Bruno has not been socialized well with other dogs, which does tend to make it difficult to introduce him to other dogs. Try introducing the dogs in neutral territory - like a park. If it's not their house, then they will be much less likely to fight. While having the muzzle on does add security, it can make the dog act aggressive. Same can happen if you are holding the dog or putting tension on the leash. The best and safest way to introduce them would be at a neutral place with a fence inbetween them. Let Bruno off lead to explore the other dog. If he's aggressive right away, then it won't work. If he's not aggressive and seems interested, then the next step would be to introduce them while walking on lead or in an open area off-lead. This is a bit more risky, so just make sure you're nearby to break up a fight, but don't be overbearing (i.e. holding the lead tight). I hope that helps and all goes well.

You will likely need to separate the new dog from the 2 "older" dogs for a period of time. Spend time with each separately, but make sure that they cannot see the new dog, i.e. keep him in a separate part of the house behind a closed door for at least one to two weeks. Then you can allow them to see each other, but not have contact. Move slowly, from this phase on to allowing them to see and smell each other across a barrier such as a baby gate. Finally, allow them to spend supervised time together. Reward good behavior with high value food treats (i.e. bits of cooked chicken) and go slow.

You're right that there can sometimes be problems when introducing two dogs for the first time, especially if either of them has any history of aggression towards other dogs. I would recommend introducing them in a neutral place at first, like a park. Keep both dogs on leash, let them sniff each other briefly, then go for a walk together. This allows the dogs to get used to each other's presence without feeling pressured to interact. After the walk, take them both home and into the house together and if things are going well, let them off-leash to relax. If things don't go smoothly, it would be best to get help from a veterinary behaviorist (ideally) or a good reward-based trainer who can work with you in person. You can search for a behaviorist in your area here: www.dacvb.org or a qualified trainer here: www.ccpdt.org.

Any introduction should be done gradually and on "neutral" ground. You can use a pheromone product such as an Adaptil collar to decrease anxiety or aggression. Introductions should start with Max being able to hear and smell a new dog but not see him. This can be done a friend's house or perhaps a family member's home. Again, some place neutral to both dogs. Once he is acclimated, he should be able to see the new dog but have no physical contact. This can be done using the fence at a dog park. Eventually, you will be able to physically introduce Max to the dog. Use a leash on both dogs for safety and muzzles if necessary. Go slowly, don't force him but correct any negative or aggressive behaviors immediately. Praise and reward him as he progresses.

I strongly recommend you both enrol in some socialisation/obedience classes in order to form some more appropriate patterns of behavior around other dogs in a safe, supervised environment. You are right to be cautious about use of a muzzle only in this situation as although it will make things safer for the other dogs it will do nothing to retrain and improve the underlying issues

Separate them for a few days then gradually reintroduce them. First with a door between them so they can hear and smell one another then separated so they can see but not reach one another and finally a supervised physical introduction. Use leash, collars and muzzles if necessary. Pheromone products such as the Adaptil collar or DAP plug in diffuser may decrease any anxiety or aggression. Provide adequate numbers of bowls, beds and toys to prevent food aggression or resource protection.

This behavior is likely to improve with time. Take them on leash walks together frequently (twice a day if at all possible). Feed them in separate rooms, as this is the time he is most likely to actually snap at her. If his behavior is not improving, consider keeping a [basket muzzle](https://www.petco.com/shop/en/petcostore/product/baskerville-ultra-black-muzzle-for-dogs) on him when they are inside so he can't hurt her. Also, if his behavior isn't getting better, ask your vet for a referral to a trainer or behaviorist who can help you. Thanks for asking PetCoach!