I have a little Yorkie about one year old and a new 8 week old pit pup. They play a little rough. Can that build up dog aggression in either one? Should I stop them if they start growling with or at each other? I'm not sure if it is just the puppy, but the pit, who is the same size as the full grown Yorkie, only the pit weighs more, is building on aggression and I do not want that to happen. Or, is this just plain old puppy play and I am being overly sensitive to it.