How do I train a horse to remain calm when a slicker or rain jacket is handled from the saddle?

The slicker or rain jacket is one of the most frequently included carry obstacles in trail competition because it introduces two separate challenges simultaneously — the handling of an object from horseback and the presence of a crinkly, billowing, noise-making material that many horses find alarming. A horse that accepts a slicker being shaken out, put on, and removed while mounted is demonstrating a level of desensitization and trust that extends well beyond the trail arena into genuinely useful horsemanship. Desensitization to the slicker begins on the ground before it is ever introduced from the saddle. Allow the horse to investigate the slicker at liberty first — sniffing it, touching it with its nose, watching it move. A horse that has freely investigated an object and found it benign approaches it with far less anxiety than one that has only ever experienced it as an unexpected intrusion. Once the horse shows genuine indifference to the slicker on the ground, begin moving it near the horse's body from the ground — along its neck, over its back, rustling it near its hindquarters — until the horse stands without concern. The mounted introduction begins with the slicker folded quietly and carried from the saddle without movement. A horse that tolerates the folded slicker being held beside it while walking quietly is ready for gradual unfolding, which should happen in small stages — one fold at a time, with pauses between each stage for the horse to process. The crinkle noise as the slicker unfolds is often more alarming than the appearance of the material, so pausing after each unfolding movement until the horse relaxes before continuing teaches the horse to process the sound rather than react to it. Once the horse accepts the fully extended slicker being held and moved from the saddle at a walk, introduce putting it on from horseback. This movement is the most alarming stage of the obstacle and should be introduced only after all preceding stages are confirmed.