Introducing a New Dog
If you've purchased a puppy or adopted an adult rescue, you want the initial introductions to your older Chi to go as smoothly as possible. One of the best ways to introduce two dogs to each other is in neutral territory. For example, try to have the pair meet in a park or on the sidewalk in front of someone else's home. The reason for picking a neutral location is to allow the dogs to meet and greet each other without the older Chi trying to protect her home and people from this new intruder.
The advantage to arranging a meeting at a fenced-in park is that the dogs can meet off leash. This makes the meeting of the dogs less confrontational. Apparently, being joined by a leash to an owner often gives a dog the feeling that she must protect her owner or, if she is timid, the frightening sensation of not being able to escape.
Another way to introduce two dogs is to bring the new addition into your home when your older dog is not home. This is the same method used when parents are bringing home a newborn baby. Keep the new dog in your home for several hours or even a day before bringing the older dog home again. With the new dog's scent already in the home, the older dog is not as confrontational as he might be if a new dog crossed the threshold to your home.
Supervise the two dogs whenever they are together, and never leave them home alone without crating either one or both dogs. Until the dogs have accepted each other completely, which may take several days or even several months, anticipate that they will have a few squabbles. The worst of the squabbles will naturally occur when you aren't home, so you'll have no idea what led up to the situation except that you have two injured dogs.
How will you know when your Chis are cohabitating well? They will play together nicely, and when they're not playing, they'll either cuddle up next to each other or completely ignore each other. What you don't want to see is constant picking by one of the dogs or an overly excited sustained interest in the new Chi. If you see any signs of predatory behavior in your older dog (stalking, creeping, intense staring, body stiffness, or rigidness), safely separate the two dogs and seek professional help from an experienced trainer or animal behaviorist immediately.