Yours are nice guys, but I'm not going to lie. My horse is the best. I didn't even have to teach it to her!
It goes like this. I put down shavings in her stall, she immediately lets go of a HUGE poop and pees...while trying to walk in order to wet as much of the bedding as possible, then paws it if it isn't messy enough. She does it every time without fail. Its like she knows I love cleaning stalls and buying tons of shavings or something!
Ok. Maybe not. Honestly though, I make a point not to teach my horses tricks unless they're useful. My filly knows a lot of verbal cues such as "back" (step back), "step" (step onto platform/into trailer), "wait here" (stay where I put you and don't eat/move away until I say you can) "ok" (this is her release word), "over" (yield whichever part of her body that I touch) and "up" (lift hoof. Admittedly this one was not a very good idea because she lifts her leg quickly and it has made a lot of people think she is offering to kick. I know she isn't, but someone else? Not so much. It wasn't very smart on my part).
Other than that I just expect her to be a horse. I always thought it would be cool to teach a horse to clean its own stall though...if they can dirty it in 2 minutes flat, they should be able to clean it too right?!