The key to introducing your Pit Bull (especially if they already have a tendency for dog aggression) is to have the dogs meet by taking a walk in a neutral area (i.e. somewhere either dog has ever been before). By walking in a neutral area you minimize, if not diminish, the risk of one dog exhibiting any type of territorial behavior. Before going out for the walk, be sure that each dog is properly fitted with a properly fitted collar and sturdy leash. It is not recommended to use choke chains or prong collars when going through the introduction, as you risk injury to your dog if a fight does break out.
While walking, make sure to let the dogs naturally walk next to one another. Both handlers should maintain a firm hold on the leash, but the handler should try and let the leash have a slight U-shape to allow the dogs to get close to one another. A tight leash communicates tension to your dog, and can lead to issues depending on how sensitive the dog is to this type of walking. Face to face contact between the dogs should be avoided at first, and you should walk parallel to one another, allowing each dog to take the lead at regular intervals every few minutes. Never allow your dog to greet another dog if they are dragging you on the leash, this will just reinforce a negative behavior and tell your dog it is ok to misbehave when approaching new dogs. You need to make it clear to your dog that you determine the who, where and when of meeting.
If the dogs appear to be tolerating one another, you can allow them to briefly sniff one another – not face to face, but using a “T shape” where one dog is able to sniff the midsection of another dog, being called away by their owner after a few minutes or at any sign of aggression. Signs of aggression to watch out for include stiff posturing, lunging, lip curling, growling, lunging, hair standing up on back, air snapping, tail between legs, submissive urinating, and freezing. The introduction should be stopped immediately if either dog exhibits any of these signs of aggression toward one another.
It might be necessary to take multiple walks, in different locations, over a prolonged period of time before the dogs adjust to one another. Multiple introductions in this manner give you a better read for how the dogs will do, and this process should not be rushed if the dogs seem unsure in any way. Stop the introduction if either dog is showing signs of fear or aggression. By interrupting the dogs before things become highly elevated, you can preserve the possibility of a successful interaction at a later time.
Once the leash walk introduction proves successful (remember – this can takes a long period of time, not all dogs adjust to one another after one walk) you can move on to a fenced area and begin to introduce the dogs off leash. One handler might work obedience with the leashed dog, while letting the other dog roam around, allowing them to get used to each other’s presence and scent. The best way to go about this is to have the resident dog is loose, while the new dog remains leashed. This gives one dog the ability to safely check things out and move away as needed while you maintain control of the other dog. Make sure the yard or fenced area is free of items that may possibly trigger a fight such as toys, food, bones, etc.