Another Timid Cocker

Question
I have a year and a half old male Cocker.  He is a very sweet dog, and to my knowledge never abused or neglected.  However, almost every time he meets somebody new he growls at them and backs up or runs away.  I don't think he would ever bite anybody, but people don't think he's friendly when he growls at them.  It seems that he does it out of fear.

Is there anyway that I can break him of this?  We've tried taking him to Dog Parks, PetSmart training classes, and other similar places to socialize him, and even try to take people's hands in our hands to show him its ok, and he still does it.  Is there anything else we can do - we want people to be able to come up and meet him without him growling.

Thank you!

Answer
He may not have had enough exposure to strangers before he was 12 weeks old.  When strangers come around, eagerly greet them.  Make a show of being happy to see them.  Be very matter of fact with him.  Don't be solicitous, rewarding him for showing fear.  A great technique if to give the person treats to give him. I have even carried a 35 mm film canister with kibble in it to give people when one of my puppies went through a fear of people stage.  Give him some time and do not push him.