Desensitizing a horse?

My gelding came from an abusive situation and I had been slowly working with him over things. After he flipped out over a western saddle squeaking some one offered to help me desensitize him. We started with his saddle pad going on and off as he used to be scared of it, then the lunge whip touching him all over and being moved around, then a big plastic bag, grain bags put on him, a lead rope hitting his shoulder, walking over tarps, tossing dog toys all around him and having 1 or more dogs take off after it, tossed the dog toy at him an by his feet. He just stands there, I've skipped around him, jumped, and made sudden movements. He's doing a lot better but he is still terrified of people, at a show this young girl came up to give me his ribbon and he acted like she was going to kill him and not even 5 minutes later another young girl came up and was petting him all over his face and he just stood there. Some times he freaks out and other times he doesn't so I'm not sure what to do for it. Also any other things to use to desensitize him to?