Goal: Horse stays off treat pouch no matter where it is on your body for one minute, the presence of the pouch is the cue.
Place some low level treats in your treat pouch and keep out for each of your horse. Start by practicing a set of 5 'Food zen' with an open hand to 10 seconds.
Now, present your pouch off to one side and in front of your horse to sniff. C/t if he moves his head away as before. Move the pouch around on both sides of him as you did your hand.
Increase the duration of food zen until your horse can 'leave it' for one minute, then start again at a lower time with a higher value treat. Work your way up to high value treats in the pouch as before.
When he is consistent with leaving the pouch alone no matter where you hold it, place the treat pouch in its regular place on your waist and let him sniff. C/t as before for leaving it. Add duration. Add value of treat.
Move the pouch to a different location on you, such as on your hip, stomach or turned behind you. When he can leave your pouch alone in any postion for one minute, you are ready to move on to training other behaviors. Keep adding duration.
As you train with him on other behaviors, peridodically c/t him for holding himeself back from your pouch. If he goes back to mugging your pouch, stop what you are training and go back to the basics with food zen to remind him of the behavior you want. Avoid lumping by training him other behaviors when he has not yet understood that he must not mug you.