Ok it's not these horses that are the problem, or maybe not even these ones particular riders. But the horrible truth is that most often, tiny reining horses are ran in competitions ridden by large men weighing wayyyy too much for their legs to support while doing so much work. The result is that horses must retire at a young age due to injuries/soundness issues. It is extremely sad! Stop riding horses you are too big for! Or at least don't vigorously compete on them
Teaching your horse how to cross over a tarp gets him used to stepping onto an object that moves and makes a noise. Anytime your horse will respect and trust you to move over something that moves and makes a noise, its a great sign that hes using the thinking side of his brain.