Catch him, put in trailer, move across the street to tall enough enclosure, geld.
Just trying to help out, not my place.
We have another option, I was just hoping we could knock him out with feed.
Corralling or roping is not going to work.
Cowboy method.... set up a good sturdy portable round pen and start feeding him in it for a while, then one time close the gate and lock him in? Then later on you can begin desensitizing him and get him gentled to halter him.
The vet who will be doing the castration ought to be able to provide some input. Perhaps use panels (borrowed, if none are available) to herd him into the trailer, then more panels to crowd him into a space where the vet can get a tranq into him at the place where he'll be gelded. Could you find out if anyone has asked around for vets that will work on unhandled or problem horses? Do you have a local humane society or animal control that might have suggestions on handling this horse?