Biting Dog

Question
I have a german shepherd that is a year and a half.  He is a wonderful dog to the family but is very very aggressive towards anyone that isn't in the family.  He has bitten my youngest sons friends twice drawing blood.  One was bitten on the calf and the other was bitten on the elbow area.  Also, when  friends come over he will get right up on them and bark aggressively.  When they turn their backs on him he will nip them on the butt.  I am very concerned about his aggression.  When I take him for walks, or car rides he won't let anyone come near me without acting like he is going to bite.  I love him very much and have had him since he was about 4 weeks old.  He follows me everywhere and I mean everywhere.  If I'm in the restroom he will open the door to get in.  I did enroll him in obedience class to socialize him, however we we're asked to leave and come back to do individual classes as the instructor was nervous about having Max in her class because of the way he acts around other dogs.  I had him neutered when he was about 8 months old because he had cryptorchidism.  This however hasn't helped in his aggression.  I understand the top dog position, and he totally respects me except when he feels the need to protect the house or any of his family members.  I was thinking about getting a shock collar, but have mixed feeling about that. DO YOU HAVE ANY THOUGHTS ABOUT THIS????????????  Thank you and I'm looking forward to hearing back from you.

Answer
This is a severe problem that must be remedied soon.  Did you go ahead with the private lessons?  I don't think the shock collar is the answer, but I think you need more help that over the net.  I think your only hope is a good private trainer or behaviorist.  See if your vet can suggest one.