You could try clicker training it? I know a lot of people don't like clicker training but I've found it really useful for reactive horses. You can use a bit of the horses daily feed or a low cal treat if you're worried about treating.
You can put a rope around his leg just below the fetlock and lift it up with the rope 1st. It will make it a bit harder for him to get his leg back and learn he can't get out of it and nothing bad will happen to him
Get him checked by a vet to make sure nothing is irritating him
Use treats run your hand down his leg every time he doesn't lash out give him a treat after awhile of donig this he will get use to you touching his legs and pick his feet up. ( this work for our 2yr old who would even let us touch her legs without getting angry).