I would try to bring different desezsitizing things to the barn with you, like tarps, flags, big bouncy balls. Anything that you would think would spook him. Work with him on the ground with these things, sometimes you may find it to be fun. Like some of the other posts, you can't desenstize them to everything, but sometimes, that is not the whole point. Sometimes it is just a matter of your horse to trust you enough to get him/her through something scary.
As for the head shyness, I would take something that resembled a bag, like a white rag. start by rubbing the horses neck with it moving it closer to the head. When you hit a spot that makes him nervous, stop and continue to rub him in that area until he relaxes and stops moving his feet. Once he relaxes and realizes it is not going to kill him, retreat and rub somewhere else. Then repeat it trying to move closer to the facial area, ears chin, etc. Once you are able to rub hi whole face with the rag that doesn't make much noise, try it with something that does, like a plastic bag. Obviously, don't put yourself in any danger when doing this. Most horse, will tolerte it and actually learn to enjoy it. I was told once that horses love to be rubbed over there eyes and I never believed it until I tried it on my horses and they both love it. Of course neither one was really head shy.
Doing it this way may take a little longer, but sometimes it is better to take time with something so important. Hope this helps. I also found a good clip from CA about this and will post it for you.