Few weeks ago a police officer was looking for a former tenant that skipped bail and robbed a liquor store. My father waved him out back to talk to me about him, and my dad didn't realize my German shepherd was out back with me. When the officer entered the gate my shepherd barked and ran towards the officer and sat down.
The officer didn't even make a move, he just stopped then went to pet him. I jokingly told him "he wants food, he won't bite but if you refuse him some food he probably will".
He's not trained period. He deals with tenants all day long long, some even feed him. I don't want him as a guard dog or attack dog, simply he has his own personality.
I've seen what he will do if you raise your voice however, I think its along the lines of "I will tear that bellybutton up".