How does Clinton Anderson desensitize a horse to a tarp and why is the tarp a useful training tool?

Clinton Anderson uses the tarp as a multi-sensory desensitization tool because it combines three things horses commonly find alarming: unusual visual appearance, unexpected noise when it moves, and an unfamiliar texture underfoot. A horse that is genuinely comfortable with a tarp has addressed several categories of fear simultaneously, which tends to generalize to other novel stimuli more effectively than single-stimulus work. Anderson's tarp desensitization begins with approach and retreat — starting with the tarp folded small and held still, allowing the horse to sniff and investigate it at its own pace. He never forces the horse to put its nose on the tarp or stand on it against its will; he allows the horse's natural curiosity to bring it closer. As the horse becomes comfortable with the small, still tarp, Anderson gradually unfolds it, then begins to move it slightly, then more dramatically, then allows it to make noise. For teaching the horse to walk over the tarp, Anderson places it flat on the ground and uses his Sending Exercise to direct the horse across it. He does not pull the horse across the tarp — he sends it forward with energy from behind and allows the horse to make the decision to step on it. The first steps may be tentative and Anderson releases the forward energy the moment the horse makes any attempt to approach. Within minutes to an hour depending on the individual horse, most horses will walk across the tarp calmly. Anderson then progresses to having the tarp draped over the horse's back, neck, and hindquarters while the horse is moving — preparing the horse for rain slickers, blankets, and any other draped equipment. Each stage waits for genuine calm before progressing. Anderson notes that horses desensitized to a tarp systematically typically show faster acceptance of other novel objects throughout their careers because they have learned that investigating unfamiliar things leads to release and rest rather than escalating pressure.