Rocky times (Updated)

So, I rescued a horse about 5 years ago. His name is Rocky, and 6 people had attempted to start him by the time he was 6 years old. I was number 6, and I only got the opportunity to do so by promising that, if it didn't work out by the end of the summer I would drive him to the livestock auction myself. It did work. After 3 months, he was stuck to me like glue, and would litterally do anything I pointed him at. One time I walked him up to a giant log (chest high to him) and, because I didn't ask him to stop he started over it. Not jumping, but walking. The poor thing got high centered because I didn't ask him to jump it. ever since that day, I was mindful of being clear with my directions to Rocky. He was so badly abused and fearful when I got him, that re-homing seemed unlikely, but at the end of the summer, I found him a home in Oregon. I drove him up and they got along great. Last year, they called me and wanted to give him back. They had too many horses, and if I would take him, he was mine. He is mine. I also have too many horses, but, with Rocky's violent history, I would NOT let just anyone take him. So, I have been conditioning for endurance with my friend Elly, and half leasing Rocky to a woman I give lessons to. Everything has been fine... then there was yesterday. After a nice slow ride with elly and Jasper, I decided to do some arena work with Rocky. It went okay, he was wiggly, but I haven't asked him for much straightness lately. Then, when I asked him for a canter, everything fell apart. Not just at the canter, which he took like a champ, but when I asked for collection, he shut down. Got mad even. Fought contact, and refused to perform. Then he planted his feet and started rearing. NOTHING that a horse does pisses me off more than rearing. It is nothing but a terrorist act. The problem is he has NEVER EVER fought me in any way. I was dumbfounded and heartbroken. So, after a near death experience for my right arm (which got tangled in my right stirrup leather the third time he cam up and my foot flung the iron out and up), I got him calmed down at a walk. Then, I set him up in a chambon and lunged him where I discovered that he won't take the canter with his head down. Aha. found the problem. I know that no one is perfect, but it is heartbreaking to find that such a heroic little horse felt that he had to fight. He is normally so passive, and he must have felt so trapped. So, my goal is to canter him freely in the pasture until he is comfortable, then slowly add areas of collection. He is the last horse I want to fight with. Especially since he is the kind of guy who will let you walk all over him, and take advantage of him. I feel terrible that he had to tell me so loudly. I apparently have not been listening to him. Since he is okay with everything else, I asked him for more than he felt he could give. I would post his whole story (the before-I-got-him-story) but it would break my heart right now, so I'll get to that later. UPDATE: I now ride Rocky in a rubber snaffle bit. He has really become so much more elastic and finds contact much more easily with this bit. I sincerely reccomend them to anyone having head/neck/collection and/or fight issues with their horses.