Yesterday I adopted a German Shepherd from a person on craigslist. The dog was clearly neglected he was soooo aggressive, but I didn't want to leave him with his owner. he lived in a tiny house with a family of mom, dad, 6 and 9 year old boys. when we got him home it took us 2 hours to get him out of his kennel. I imminently noticed something strange with his hind legs, I think they never took him on walks and never let him interact with strange. his legs are weak and thin not muck muscles. I need to start exercising with him what should i do? take him swimming, run with him, I don't want to stress he is still not used to me. introducesing him to my other dog helped him calm down but he is still very skiddish and he does bite