With the cat, I have introduced mine to my dogs EXTREMELY carefully and it still almost got bad, not because they were aggressive towards my piggies, but because they don't realize how big they are. Their version of playful can and sometimes will kill your little bundle of joy. But, my guineas live upstairs and the dogs generally stay downstairs, so as long as I keep my door shut and their piece of the room closed off, they're always fine. I definately reccomend giving them a whole room. It makes it a lot easier to keep everything where it should be, including living everythings. I had a little boy sneak out once but he actually ended up shut out of his cage because he couldn't climb back up, he got into the corner where I stored the hay, I walked in at about 3 that morning to him crying for me to put him back. He still tries escapes every once in a while... Moral of the story: close them off in more ways than just the cage if you can. You might be really glad you did...