I agree with smrobs on that one...if you can sit out those bucks do so; better yet, if you can push the horse through them by getting those feet to move out, do so. A horse bucks basically because his feet are "stuck" in place. Don't bail, think about how you can get those feet moving foward. Sometimes all it takes is taking one rein to your hip and disengaging those hips, and then using your reins, or someone on the ground (if the horse knows round penning techniques), to ask for forward motion.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."