My two year old female tries to one up my old lady every once in awhile!!!!! I do think it's the age, they're the teenagers moving into adulthood so they are testing their boundaries. I just make sure that Issy knows that Daphne is the alpha by doing little things, like always feeding Daphne first and giving her treats first. And when I'm giving Daphne attention Issy always comes in between us so now I block her so she can't move Daphne out of the way. When she does get out of hand though when she hears me call her off she does listen so it doesn't get out of hand. Since it took both of you to pull them apart maybe when he's really into something, whether it's a toy, bone or his food try different ways to get his attention. It may not work, but it's worth a try!!! Oh, and ALWAYS make him do something: sit, down, shake...., before he gets anything. Good luck