I had 3 Greyhounds and a Jack Russell when we brought home our 2 Pit puppies (Maybelline and Maryjane), I knew my older dogs would not be aggressive, but they all play really rough. If you have ever seen a Greyhound play, they can cause considerable damage. I have also seen them fight, and they have to be pulled apart as opposed to a pit scuffle, which can usually be stopped by yelling. We put a gate up in the hall to introduce and yet separate puppies from adults. We gradually let them be together (always supervised) and separated when we were gone. We did this until they were 1 yo; my daughter moved out and took Mary with her. I now have 1 Greyhound, 1 Jack, Maybelline and 1 foster, I still let Maybelline go in her bedroom when we are gone, but now it’s so my Greyhound doesn’t teach her to counter surf. I guess the point of this very long story is this, it took awhile but we didn’t give up, and our cautiousness paid off by no injuries, and a happy well adjusted pack. By the way, all of the dogs Love Maybelline and love to play with her, she is the favorite of all my pack.