Fear aggression is the worst type of aggression in dogs. But the good news is it can be eliminated. There are several types of aggressions. Some cannot be reversed, merely maintained. From experience, I can say my success rate is 98% and I have had other trainers in other states agree with me. A book called “Grrr! The Complete Guide to Understanding and Preventing Aggressive Behavior,” talks about all types of aggressions, specially fear ones. I recommend it. But aside from good reading materials, you will need outside help – specifically someone who will not baby your dog! Someone who will establish what he does not have right now: TRUST. Find a gentle, experienced trainer/behaviorist (ideally a combo, do not settle for a behaviorist! You need someone who is hands-on, not a person who talks about how the dog COULD change). Also, be aware this will take time. It took a long time to create the fear. It will take a long time to create the trust. Do NOT push socializing right now. It could hurt more than do good. Just take your time. Give your dog love, and learn how to teach him to trust. Eventually,enroll him then into a Group Class, as it will have a major positive impact! But that’s a step to take later in the game. Right now it would probably make matters worse.