Yes, done properly (as in within three seconds or less of the bite), popping him can be an effective reprimand. Any longer after that timespan and the pop will do nothing but confuse him. Ideally, if he bites, INSTANTLY pop/squeal, and then put his feet to work and get some sign or respect from him. Either back him up until he is listening/backing willingly, put him on a circle and do some NH lunging (with lots of directional changes) until he's giving you one of the signs or respect/relaxation (inside ear on you, licking/chewing, etc.). What you're telling him is that it is a very bad idea to bite an Alpha horse (you), and that you will push him out of your space and make him work more than he would like to if he tries.
My guy has a tenancy to nip very quickly if he is nervous, it's a very sudden thing and takes less than a second, so it's easier just to try and keep him relaxed in the first place. On the other hand, he also nips me when hes bored. When he does that, he gets a pop on the corner of his mouth.
Sounds like your guy might have just gotten a little exited about trotting. I would have jerked the lead and yelled, then taken a closer hold to his head on the lead rope for better control, and tried again.
I go by the 3 second rule, if I can discipline them within that time frame then do it, otherwise forget it. He didn't do it because he was mad at you. It was probably more of a "I don't want to run anymore and you can't make me" gesture.
One of mine came running at me, bit my arm and knocked me on my butt :lol:By the time I collected myself, it was too late to do much of anything. I still have the scar from that bite. Be glad it wasn't in the face or someplace where a scar would be more noticible.
One of my geldings used to have a biting problem as well. Punching, hitting, or attempting to physically harm the horse doesn't do much good. Horses are big, people are little. I don't know about you, but if a little kid who weighs a 1/10 of my weight came up and punched me, I wouldn't be too alarmed. Too often, the "pop-him-back" technique turns into a dominance game for the horse. And guess who will probably win? The horse.
Instead of trying to hit your horse, make him move. With my gelding, I stood my ground, looked as mad as I possible could, and MADE him back up with my voice while swinging the lead side to side (from his groudwork, he knew this meant back up). After he has backed up so I am out of his reach, I let him stand there and think for awhile. He can't move towards me--he needs to stay where he's at until he has camled down. Then I walk up to him and we do something he is good at, such as turning his hind end away from me with a swinging lead rope. Then I have a reason to praise him for something (no food--pets and vocal praise), and he is my best friend again.
In the horse world, the leader doesn't move unless he has to get his point across. The ears go back, a tense posture is adopted, and the other horse backs off. Just think of yourself as a stubborn broodmare who doesn't allow biting, as a horse trainer once put it. Also, you may want to stop giving treats from your hand--put them in a bucket.