Hate to disagree with you wildspot but a horse can only rear when its stopped, if its actually moving either direction it can't rear, I just think that pulling on a horses mouth is often something that can lead to rearing and that is why people say you should make them move forward, but if pulling isn't the reason for it and an obstacle is then I use backing to get them through it. Some people kick and pull resulting in rearing but I know this technique isn't for every rearing situation, I would only use it if they were spooking at something, that way I acheive the get in front of my leg agenda along with the lets go this direction agenda, but poorly executed it isn't a good idea. Maybe it shouldn't be suggested if you can't supervise the rider trying to do it or if you don't know their level of ability.
Troubled TB ~"A thorn by any other name will prick just as deep." @-'--,---