I've raised German Sheperds, and Doberman Pinchers. There is no excuse for haveing a mean biting dog. There is a huge difference in a protectve dog and a mean dog looking for trouble. The owner should have taken care of this dog a long time ago. Unless he's told to bite, or protecting me or mine from a direct threat. He better not bite. My son learned to walk hanging on to the Dobes collar or tail. I was raised up with German Shepherds. There are lots of people that think a dog has to be mean to protect. Look for intelligence, temperment,and willingness to please. Not willingness to bite first. I hope your son come through this OK, not afraid of every dog he sees. Go to Wally World and get a wrist rocket,and a bag of marbles or steel balls for it. Those hit like a .45.