Using the pennies or the squirt bottle may be making him associate people with a bad experience. (meaning that, when he sees people, he's going to hear an unpleasantly loud noise or be squirted with water), which would definitely not be what you want. I would keep him on leash when introducing him to new people, and just have the person stand still (not trying to pet him or even pay any attention to him), and just let him smell the person and "get-to-know" them before they start petting him. If he starts trying to back away or bark, just give him a little jerk of the leash and say "no" or whatever negative feedback you like to give the dog. When he accepts the person, give him praise. He'll soon learn that it is unacceptable to be afraid/bark at new people. Hope this helps!
BTW, I don't know if you've done this before, but when he is fearful of someone, do not pet him and tell him its ok. That only reinforces the behaviour. :)