Here is the thing if you did have them haltered dragging the lead, they have sore heads and have been learning to stop when they feel pressure not move forward when they feel pressure.
I would tie him up each day and only lead him to water and feed. Kick him loose only at night. Once he figures that the only way he is going to get to the water is if he leads, he'll get it quick. Start by watering him while he is tied, once he gets used to the bucket move it farther and farther away each time. Do not get into a tug of war with him you will loose, try pulling and releasing on the halter and once he starts moving make sure to release the pressure. If he does not fight the lead while tied I would start tying him with his head up for 15 minutes and work your way up to 2 hours a day. Stay around so if something was to happen you can free him and make sure your knot is one that releases easy. It helps to have a knife around just in case you can't get the knot untied.
Take your time and do not get frustrated in the beginning it seems like you are getting know where but just be calm and persistent you will win in the end.
The tarp, if we had a that horses that reared allot we would through the tarp over his head once he went all the way over, they just lay there and think they died, after that most would never rear again.
Good luck