My boyfriend's cow horse is like this. I HATE IT. He is the boss in the pasture and only accepts being caught on his terms. To make along story short, what has worked for him is to acknowlage him first whenever we go into the pasture for anything. If we go to catch another horse or to feed or water, whatever, if Pistol comes up he gets a good scratch and a treat if i have one. This way he is not being caught everytime he sees us and we usually mean something good to him. This maybe a little too deep but i think it also acknowlages his place as boss horse and makes him a less resentful when we play with others in the herd.