Thanks, Connie, and trainer, for the fast reply.
I guess I have to explain a bit more about him. He came from a man who "is the only one who can lead this horse out to the paddock", so he never learned correct behaviour. And he was lead, as Connie said, with leadshank and Chiffney bit. And with the chain through the mouth and under the lip. That only led to a bleeding mouth in one case and a former owner even more macho......
I thought I had it cured the first year, with my carrot treatment, he went in fine, waited to be unhaltered, took his carrot and took off. The trigger for this now dangerous behaviour was him bolting off, me not being able to hold on, letting him go. And bam, there he had learned that he can get away if he pulls hard enough. That's why strong men can hold him. I sometimes don't even try anymore, since he hurt me before, just try to get him IN the paddock, since he also tries to take off about 50 meters before, depending on when he was out last. The backing up way before the paddock gate helps a lot, gets his mind off the running a bit. He is not really trying to get away from me, he's just so full of energy that he can't hold back long enough I think, just has to go, go go. On the way to the paddock he does some antics, too, jumps back and forth, circles, snorting and blowing, tail up, but he doesn't try to get out of hand. And for some reason I hold on to him no matter what . Maybe because I know I CAN'T let him get away, it's dangerous.
I think it's not so much the horse, it's me who has to get over the letting him go phase and just hold on to him. He's just taking advantage of my weakness. He's a supersmart horse who does something new, and the second time it's already a habit. I was actually thinking about putting up some kind of a little holding pen in front of the paddock, 12 x 12 ft, put him in there first, unhalter, THEN open the gate towards the paddock. Maybe that breaks the habit of bolting off?
I do lead him now with a snaffle bit, lead rope slung through the inside bit ring, not through both rings, and not hooked up and fairly loose and when I have to pull, it's a short jerk and he comes around with his head towards me. Matter of fact, most of the way out, after a day in anyway, he walks with his head and neck towards me, two tracking with his hind end.
After all his jerking and pulling, and of course, hurting himself, he still takes the bit eagerly and is soft in the mouth, gives nicely to very little pressure.
I titled the threat "exuberant trotter", because that's what he is a bit exuberant and anticipating. He also needs, in my opinion, a herd. I have a small one, but with a laminitic mare, and the poor girl would get hurt with all the running and playing he will cause. He's. by the way, very friendly with other horses, I never seen him pulling ears back. He's always asking for wither scratching, plays with me out in the paddock, hide and seek and such stuff. I make it a point to initiate it, of course, and frequently have to put him in his place.