Hello, new here. I have a 2 yr old male "Bruno" he is a great dog lives with a cat, a female GSD, a beagle and yorkie gets along with all. He has growld at step son just once or twice. He is typical GSD for he is leary of new people. My problem is if some one gets down to his level ie; in his face, even to just pet him. He will, and not always, and not with everyone, will suddenly get a very low growl which will quickly increase very aggressively After several visits to the vet , he now this last time did not like his visit there. He laid and listen very well in waiting room even let a couple of people pet him on the head, there was a nother lrg dog there trying to get aggressive with him and he didn't even flinch. But when the vet came around the table...well I was glad I was the one that had control of him And he took me by surprise with the aggression he shown that day. Now I have young kids nieces, nephews etc that are right at his height and he doesn't seem to bother them at all...he will lick them in the face, but no aggression. So anyway, whats up ? not enough excercise? And yes, I do have exspeirience with GSD's have had them for 13 , 15 years. But never had one so unpredictable.