has anyone had problems with their american bulldogs being people aggresive? murphy has not bitten anyone, but every now and then, he just kind of freaks out, and barks and growls at certain people. yesterday we took him to a festival, and he was great all day, and then this lady was petting him, and he all of the sudden just started barking at her, and acting like he wanted to bite her. what do i do in this situation? is this a common problem. he's a 10 month old neutered male.