My mustang was a difficult horse and did the rearing and striking thing when lunging. His “tell” on the ground would be pawing - he wouldn’t just rear and strike out of the blue. So while grooming him or asking him to do something, if he started pawing, then I’d know what was next if I didn’t re-direct him. But really, it started before that.
There are many signs that a horse is going to misbehave before they actually get to that point, so you need to step waaaaaayyyyy back and look at his behavior in each moment and decide - is he with me or not? If you can get him with you before his behavior escalates, then you are going to have a better time training him.
I’ve worked with a couple amazing cowboys who have helped me in this regard. Look up Harry Whitney and see if you can read anything about him. The other person is someone that probably nobody has really heard of, but he is along the same lines as Harry.
What they taught me was to get the horse’s thought to be with you. Before even taking any action. Before leading or grooming or riding or any other sort of thing you want to do with your horse, you need to have their attention. It is especially important with this horse of yours since he seems to be so herd bound.
With a horse who is prone to striking and rearing, using backing up as a method of discipline is going to work against you and will only reinforce that bad behavior, because I’m guessing that when he goes up or lifts a hoof to you you release the pressure and let him go in order to keep yourself safe. FORWARD is always the answer for a horse who wants to go back and up.
Do you have a round pen? If so, use it. Get the horse in there and get his attention on you. If he can live in there for a while with water and you come out to feed him, that is fine. Whenever you come around, his eyes need to be on you. Whatever you need to do to get his eyes on you is okay. You can jump up and down. You can slap your hand or a rope on your knee. You can make funny sounds. You can wave a tarp or a flag in the air. You can jingle a bell. Whatever, it doesn’t matter. Once he gives you an indication that he’s paying attention to you, relax and release that pressure. The first indication could be an ear moving. It could be a look in the eye. It could be turning his head to look at you. If he looks away, go back to making yourself be noticed. This doesn’t have to involve running the horse around until he “gives in.” The chances of you getting a horse like this to outrun his anxiety are slim - you must have impeccable timing and release. With this method, you could move around the outside of the roundpen while he’s inside to start. Whenever he takes his eye or attention off of you, move, stomp, clang, whatever to get it back.
Once you are safe and have a better read on his body language and know how to get his attention, then you could move inside with him. Again, do what you need to do to get his mind on you and not outside the pen. If you had his attention and are standing near his shoulder (but not near enough to get in the way of any feet) and he looks away, move back toward his hip and see if you can draw his attention that way (again, staying out of any striking range). If he turns toward you, then release and pet him of speak to him softly. See if you can build on the time you have his attention.
I would not run a horse like this around. I would not back up a horse like this. I’d first try to work with him in a round pen and on the ground with just getting his eye and attention. Do a little of this multiple times a day (don’t go on and on for an hour or two - you want to create a foundation you can build on) so that it reinforces his focus on you.
When this is good then you can proceed to putting on a rope halter and walking with him or lunging him or circling him, asking him to give to pressure and engage that inside hind. Or you can send him out and ask him to walk a circle around you and pay attention to you.
It is going to take a lot of ground work, a lot of time and effort and attention and practice. For someone to watch for ground work, I like Buck Brannaman’s 7 Clinics DVDs, and I know others like Warwick Schiller’s YouTube videos.
I would also recommend finding a good “NH” trainer to help you with this. Be careful whom you choose because there are a lot of charlatans out there. If someone can help your horse and teach you at the same time, that would be best.
Working with a horse like this is not for the feint of hart. It takes a lot of determination and perseverance to want to learn how to get the best out of the horse.