he needs a paradigm shift
looks like you have lots great tips from lots of great horse folks like yourself. problem is your still having the same problem and / or creating new ones.
try this, it's what i call a paradigm shift.(a paradigm shift is how you think) lead him into the arena and try stopping just before you think he is going to stop his feet. now turn him 180 degrees around and lead him back out of the arena, to a place he is more comfortable, (say in the aisle, next to the stall etc. it's time now to put him to work (change his thinking). take hold of his kead rope right up next to the halter and have him to begin moving his body around yours, 3 circles in each direction and slowly release the lead and allow the rope to slide through your fingers so he gets farther abd farther away from you. if he isn't going like you want him to, just move your hand back toward his halter. he should do this without any resistance and get better and better at it with each time you change directions. when you are longing him on a 8 foot lead you can stop. gather him up and head back to the arena. this time he will gladly go further, but don't let him trick you into not having to do some work. turn him again and repeat this about 3 or 4 times. by then his paradigm i=has shifted from, I'm more comfortable in the aisle to I'm more comfortable in the arena and you never had to pick a fight with him, hit him or take a chance he would hit you or someone helping you.