I have a QH that is a rearer. I've had him for almost 21 years. In my opinion, there is no "cure" for the rearing horse. Here are things I've done over the years.
I have done the "pop a water balloon" and the "break an egg" over his head routine. You have to do it WHILE HE'S IN THE UPWARD PATH and not when he's coming back down. It's hard to get it just right... it's messy and harder then you would thing. The thought behind it is that they think they are hitting their heads and that makes them a little more careful.
I have yanked him to the left or right while he was in air, that knocks him off balance and forces him to throw his feet back down. You have to be careful because if he's smart, he'll catch on and when he go's up and you lean forward to yank that reign, he'll spin the opposite direction and you'll go flying.
I have also kicked him forward while he's in mid rear but then he leaps really high and it's a ride, but you do get him moving forward.
The other things I've done is jammed my knuckle into his spine just above the withers. That must cause discomfort because that keeps the rears low, around 18 inches.
Obviously the tie downs are the best option, I used one that was a thin plastic coated wire that I got at a tack shop. He got to where as long as he knew it was there, he wouldnt try anything. Lastly I cut then end off a broomstick, about 12 inches worth and I put a handle on it and hung it from the saddle horn, when he went up. I bopped him between the ears on the upward motion and that brought him down.
I know my methods seem cruel but they arent. Rearing is the most dangerous thing a horse can do and it isn't something to play around with. I never found a true fix for it. But I found a lot of work arounds and my horse and I have had 21 years of fun together. I love him and I'm not an abusive owner... I just tried every method ever mentioned. Including tying a peice of baling twine from his halter to a string of his tail. So that he would feel like he was pulling against himself. The only thing I never tried was to flip him over. I didnt want to hurt him or myself....
Hopefully one of these ideas will help you....
"Be a best friend, tell the truth, and overuse I love you
Go to work, do your best, don't outsmart your common sense
Never let your prayin knees get lazy
And love like crazy"