It really depends on what kind of buck you are dealing with... With a buck after a slip or something, I wouldn't worry about it too much, but as a rider, you should be able to feel these things coming and already have your hands up to get the head up before he has a chance to get his bum up.
That's how I tell a really good rider - not if they can sit a buck, but if they can prevent a buck. Sometimes a rodeo is going to happen anyways, but if the horse is a bit hot and a rider can ride tactfully and with good timing through it, it's far easier than dealing with a buck.
With a horse who is "feel good" bucking, I kick their little butts into high gear. Like move it buster!! That's not allowed :P
With a horse who is bucking at an aid, like the changes, or something, you have to be quick enough again to prevent the buck, and whatever comes after it. In the changes it's usually a buck and then a bolt - so when they buck you half halt them forcefully onto their hineys and keep the aid for the change on. Eventually they figure out that bucking gets them in trouble AND the aid doesn't go away.
However, if you don't have the timing for these things, I would really highly recommend getting someone on the horse who does. A poorly timed correction is worse than no correction and as was pointed out, can actually make the issue worse.
They say money doesn't buy happiness -- well happiness doesn't buy horses!