Christy,
He probably wasn't taught as a baby NOT to jump up on people, this issue should have been addressed immediately when you brought him home as a 5 month old...not lecturing you there =)
What I do because I have a 2yr old stallion who does the same, is keep a lead rope attached to the bottom ring on his halter and any time he even *thinks* of rearing, you snap down on the halter (not cruelly, just enough to get his attention) and you say "NO" in a firm voice. Once you get the handle of it you will notice even the slightest twitch he does before attempting to rear and you snap down on the leadrope and again tell him "NO" "DOWN". What I really mean by snap down is you grab the leadrope, snap down (again not cruelly) and then HOLD his head DOWN so he can't rear while you are telling him "NO" and "DOWN". He will figure out pretty quickly that you don't like it when he rears.
I often when I am by myself have to keep a foot on the ground on the end of the leadrope and then work my way around my 2yr stud colt, this way if he tries to rear he only gets his head so far up because my foot is standing on the end of the leadrope (if I need both hands btw). Not sure if it's the smartest thing to do but I cross tie him too and the cross ties are up high for large horses so they don't hold him DOWN so I need to keep that leadrope on to pull his head down whenever he *thinks* of rearing.
So far it's working great, he used to rear every day, now he only rears once in a while and soon I am betting he wont be rearing at all. I've had him for 2 months so we've progressed greatly!
