I hate to have a horse buck bc it shows that I've skipped parts of his training. :/
But, when it has happened, my first impulse is to circle and beat the living snot out of the offending horse. We circle until I decide I'm a little tired, then we circle in the other direction. I WANT my horse to understand that he just committed a felony. Then, I dismount and we school as if we are in advanced stages of preparing for the Tevis Cup!
You HAVE to punish this behavior. The bucking will just get worse and you'll just get hurt. Either you punish it, or put out $'s with a trainer to tease for a buck and punish it.
It's ALWAYS best when your horse NEVER experiences a desire to buck under saddle and just bucks out in the pasture, with his buddies.