Mac used to lake the lead and barge out of my hands from time to time, like when he decided he'd rather go back to the mares or rather not get into the trailer. He'd do it so quickly that I had not time to prepare. But, you have to be ready to stop that action almost BEFORE it happens
you watch him more closely and the minute he is even thinking about barging off, you give the halter a firm snap (and yes, definitely get a rope halter and wear gloves for this training. Or, use a chain over his nose). Get him to change the direction of his thinking so that it's on YOU, then walk forward, but keep an eye on him. the minute you see him "wandering" mentally, do something that brings him mentally back to you. you start out with a big snap of the lead and a stern veral scolding. next time, give the stern warning (in a firm voice) , and if that doesn't work, the snap of the lead. eventually, you give a stern warning when his attention wanders and he'll come back just with the warning. But, you must be ON him. if you catch his "thought" before it has wandered away very far, it is very light and easy to bring back to YOU. But, if you allow him the extra 10 seconds to really become fixated on that outside thing, his "thought" will weigh so much (figuratively speaking) that it will take a LOT from you to get it back.