If you plan on introducing them, do it through the cage. Never let them together, at least not until you know for a fact that your new pup wont use them as a chew toy. Even so, you never know what will happen next. Some dogs are perfectly fine with other animals, like rats and other small pets and can really care less when the little guys are running about all around them, but alot of dogs do have a natural instinct to kill small pets like these. My BF just got a new puppy and as of right now the pup doesnt really notice my two boys. One day he did pay some attention to them and after a quick bite on the nose the pup doesnt really care to be around the rats anymore LMAO! Alot of the time, if any other larger pets try to mess with a ratty, the ratty would win and the other pet learns not to mess with them again.