Altho I have several clickers, which I use periodically, they seem to get in the way. I've dubbed it "clucker" training as I make a cluck sound which the horse quickly caught on to. There is info on youtube where a gal is actually working with ponies and explaining what response she is looking for and when to click. You can prevent mugging if you always extend your hand so the horse has to turn it's head away from your body. You do need to spend a little time teaching your horse the concept by getting him to touch a target (tennis ball on the end of a stick or crop will do). You don't move it toward him but initially hold it where he might touch it. Click and dig out a treat. As you move it to a different place each time he will touch the wrong spot but keep still and he'll get the right answer c/t. I'd worked on trying to diffuse his fear of plastic bags for weeks using approach, retreat, over and over. If he didn't bolt he was stone rigid. With clicker training it took about 10 min. I spend about 10 min daily for several days. On the third day a bag was tied to the end of the lash on the lunge whip. No matter how I flapped, snapped and flopped the thing up over his head I couldn't get a reaction. He got a bunch of treats after that. On the fourth day, at liberty I was really energetic with the whip and bag. The look on his face was "I'd doing what you want, give me the ****ed treat", which he got of course.