To the OP, if he lifts his leg step to the side and give a good kick to his belly. Use the top of your foot and not your toe, no way to actually hurt them that way but it sure does get their attention. Rubber boots work the best if you have them as they flop around and make all sorts of extra slapping sounds. Never ever let them get away with trying to kick without an immediate and harsh reaction. At the same time give a sharp "HEY!" or some other quick, one syllable word you like. Pretty quick all you have to do is say "HEY!" to get them to stop misbehaving.
I don't agree with leaving them alone while eating. Best way to prevent food aggression with any animal is take their food away and give it back on your terms, not theirs. By not doing this you can end up with a very aggressive animal when food is involved and that is not safe. BTW, I also do it with my dogs.
Jewelsb, do not let your horse turn his butt to you to begin with. Watch him closely and as soon as he even thinks about turning it in your direction, give him that same kick to the belly. Once their butt is pointed at you, you've already lost the battle because they can kick faster than you can with a lot more damage.
That said, some animals are just rotten and dangerous. I was taught growing up there are to many good animals out there to put up with a bad one. If you can't stop the behavior get rid of your horse and go buy another one.