I have taught all my horses to “stand”. And not just at a mounting block. Stand means stand. Some catch on quickly, others take a little longer. For me this is a very black and white issue and it is either correct or it’s not. If my horse walks away when I get on, I get off and do it again. For the slow learner this may be the entire ride (getting on and off).
But when they truly know stand it can save someone from getting hurt. Many years ago SO got on my mare bareback at a show. I was packing up to leave and he was hand walking her around. To get on her I told him to use the running boards of the trailer. As he attempted to get on, he slipped on the running board and fell directly under her. She didn’t move a muscle, she just looked at him like he was an idiot. But she knew to stand still no matter what:yes: