I agree it it becomes an issue of necessity. That it is why I took a day when I had nothing to do and dedicated it to getting him to load on a trailer.
In the beginning of the day I took it slow with him because I knew he had a big fear of it from the way he was reacting. I have a feeling it might have been a previous bad experience when he actually went to get off and a claustraphobic(sp?) thing.
Whereas later in the day when I could tell he was over the fear and was just being a tool I got up him. He backed off twice with little warning and fast. Both times I made him work hard and he was only allowed to rest in the trailer. It only took those two goes for him to stop it.
Though it will be a test to see how well he goes tomorrow, hopefully good.