There are several things you can try. The first would be to put your dog in a sit-down position everytime someone approaches. I realize you cannot do this if you're walking in a busy area. The second is to practice avoidance, but again this may not be possible where you are walking. You can also have people you know walk towards you and toss the dog a very good treat so that he sees strangers coming towards you as less threatening. This takes a lot of time, and you need to have a lot of friends that the dog does not know, but you have the best chance of him getting over this with this technique. If you want to do more reading on these training methods, I have an article at http://hubpages.com/dogs/dog-to-dog-aggression, but it is mostly about dog-to-dog aggression, which is what I see most commonly.
No matter what you do, your dog might get away from you someday, and if he bites someone, the authorities will take him away and may even decide to kill him. To avoid problems always walk him with a muzzle. Keep him in a good harness so that he cannot take off on his own.