, back when I was teaching all my horses to rear, I did it with a great deal of care. My model was Johnny Bergeson, who sadly has now passed away. He taught that rearing requires a three part command. If any of the 3 words are missing, the horse is corrected. The horse can/should only rear if all 3 commands are said. And his students were told to practice NOT giving one of the words and correcting the horse if it reared.
I never had a horse rear when it wasn't supposed to, except once, which was pretty funny. My 3 words were "ready, set, hup." One time I was riding the white appaloosa around the Maryland Horse Fair and I called to someone in the show, "Are you ready?" and my appie went straight up. It surprised me so much, I never even corrected her.
My white appie went only by verbal commands to do her tricks, and when I would do a show for kids, it drove me wild because the kids would hear the commands and then start saying them, totally confusing my mare, because they were giving her multiple commands. They also would give her commands when she was in her paddock before and after a show. She loved doing tricks and would do them if anyone said the correct word.
On the other hand, the chestnut appie went totally by my body stance and movements. I could have said "banana oil" and she would have done the tricks. Since nobody moved exactly like me, nobody could get her to do any tricks but me.
Our "World's Greatest Pony" was fabulous at tricks until I got a colt and started teaching him tricks. When he saw the colt doing tricks, he never would do another trick. And won't to this day.