One of the biggest issues people have with Clicker Training is the idea that the horse will become dangerous once food is provided as a reward. However, when you train properly with Clicker Training this becomes less of an issue then someone who uses treats indiscriminately.
To put a stop to mugging the second lesson (the first is Touch Target) is Look Away: the horse is too look away before the Click/Marker and the Treat/Reward. Whenever a horse starts “mugging” (begging for treats by pushing into your space, pushing on your body, nosing your pockets, etc…), I return to Look Away and remind the horse that it is not acceptable to beg.
For example, lets say you are teaching a Head Down exercise and suddenly the horse starts mugging. I would immediately go back to the Look Away lesson. No one begs more then my mini-pony Pandora so she is the lesson horse for this video:
Tips for teaching Look Away:
IGNORE pestering behavior like mugging and begging for treats. Generally, the horse will do less of this behavior as it is not rewarded however, Dancer is very persistent because she is very food motivated. Be patient and just IGNORE and reward the desired behavior which is looking away.
Catch the moment the horse stops or looks away from the Handler or treats. Mark this desired behavior with a clicker. The reward follows and give it by holding it away from your body or even tossing into a food tub.
If the horse knows other desired behavior they might run through other exercises to see if that is what you are looking for (Dancer in this video tries lifting her forelegs one at a time as that is an exercise she knows with clicker training).
When Clicker Training, if your horse starts mugging or begging, return to this exercise to remind your horse how treats are given.