I also have a head shy horse but for some reason only when he wants to be he is only five years old, can it be that he is only testing me to see if I will leave him alone? I will use your advise and see if it gets better.
Free_Sprtd hit it right on the head. One other thing, this will take a VERY long time to fix. If you don't see improvement immediately, don't get discouraged, just keep working with him and he will eventually have a lightbulb moment.