Also to the OP, sorry your thread got sidetracked to yet another review of the movie Buck. I agree, generally, with the geld or go home statements made. This horse would be dangerous enough without huevos, the addition of them makes it worse. He doesnt need them, he was obviously never shown or campaigned in any way shape or form. Anyone who knows me will tell you I am no fan of stallions anyways, if your not going to be a breeding facility. As my grandad always said a good stallion makes a great gelding. Just ask my wife we have the argument at least weekly about out whether our stud colt remains in tact, and you can bet yer boots he is well mannered.
If you choose to keep working him as he is, I would suggest shorter sessions 30 minutes or so early and then 30 more later in the day. Giving simple clear commands of what you expect, rewarding any positive, honest effort, and quitting on a good note. Even I'm told, if that goes back to a previously learned behavior (see honey I do listen).