 He's coming out of his own. He's becoming that teenager, and he wants to be really, really protective. It's just like a kid being protective over one of its toys. This dog is now being protective over a brand-new environment away from its litter mates at this point. Now, the whole concept of the litter mate aggressive behavior is among litter mates, not once they've been separated. It may appear that way to the novice, but it's a whole different ballgame