When a horse pins his ears at me, the first thing I do is GET BIG. Stand up straight, shoulders back and look directly at him. Challenge him for that right away. If he doesn't immediately put his ears forward like he's saying, "What? Did she just get big and challenge me?", then I go in carefully, but I walk directly at him. Then I back him up to the back of the stall, without touching him because in horsey language that's dominant behaviour. I would have halter & lead rope in my hands and as soon as he's backed up, I'd put my left hand, with halter to the side of his face around the cheek area, and push his face away from me and hold it there. With my right hand, I'd toss the rope around his neck and then I'd put the halter on him, watching his mouth the whole time. Set him up for failure (fails to bite) right from the beginning by setting yourself up for success (doesn't get bit). Once he's haltered, then you lead him out of his stall and take him to the cross ties or the hitching rail or where ever you can groom and tack him up. Watch him every minute, and if he swings his head toward you say, "NO" firmly and push his head away. Don't let him even open his mouth around you, push him away and say, "No". The idea is, never give him the chance and eventually he will probably give up.