.I have a 3 year old female pit who shows aggression towards certain people in certain situations. I have not been able to break her of it because she believes she is protecting me. Pits tend to be more territorial than other breeds, especially when it comes to their humans, of whom they are extremely protective. If the people your pitty meets are afraid, your dog will interpret that as aggression and become protective. Have him wear a muzzle to safe guard both the people you encounter and your dog. Whatever you do, DO NOT STOP socializing your dog. Also, your own fear will increase his aggression. Try to remain calm while chastising his bad behavior (no physical discipline in public ever) to maintain that you are the alpha and not your dog. I stoop to her face, put my finger on her muzzle, and firmly say no. Sometimes I have to hold her muzzle to face me. She always kisses me in apology and behaves immediately. Pitties live to please their humans, like most dogs, so your quiet but firm disapproval is generally all she needs. Good luck, it has been a learning process for both me and my beautiful big girl!