I've followed my dog trainers advice, and I have never had problems since. As soon as you figure out who's the alpha, you back him up. That way, you are letting the new dog know that no one thinks he is boss. It'll help resolve their issues alot sooner. At my house, my pomeranian some how wound up being the alpha though. haha. I got worried about it a few years back and actually gave away a dog (Queensland Heeler) I really liked. My pitbull-sharpei was losing weight and I got scared. Looking back on it, I think if I would have quit disciplining the Heeler for guarding the food, and instead encouraged Rosco to wait and eat after Ricky (the heeler), they would have worked out ok.