Ok Percron/TB cross. Could you not put up an electric fence to contain, or work more often? Maybe the halters will work, you are tryng, but it is basic - contain, or work harder. You could set up an electric fence and contain.
Keeping a halter on a horse is dangerous.
Twogeldings, next time you catch your 3yr old, take it off. Next time you go to catch him, just walk him down. DON'T CHASE HIM!! It will take a long time, but when he realises you are not going to give up, he will let you come up to him, and be casual. give him a stroke on the neck, slide the rope around, reassure him, then put the halter on. He knows you, I caught a problem mare I had never met, in a 15 acre paddock this way after 1 1/2 hrs, but after that she was easier to catch.
Have done this with many horses I have rehabilitated from abuse. You are not threatining them, but you are Alpha, and in control.