What is the correct process for sacking out a horse?

Sacking out is the traditional term for desensitizing a horse to contact with objects — originally saddle blankets, slickers, and ropes — by rubbing, swinging, and draping them over the horse's body until it accepts them without alarm. Done with patience and timing, it builds a horse that accepts unusual touch and movement around its body. Done aggressively, it traumatizes the horse and creates lasting defensive reactivity. Begin with the horse in a familiar, safe space where it can move but cannot fully flee — a round pen or small paddock works well. Start with an object the horse has already shown it can tolerate nearby, such as a saddle pad or soft rope. Introduce the object at the horse's shoulder — the least reactive area of the body for most horses — and rub gently. The moment the horse stands without tension, pause the rubbing and allow it to relax. Then resume. Progress to areas of greater sensitivity: the flank, the hindquarters, the belly, under the tail, the legs, and the face — in roughly that order, since those areas tend to be progressively more sensitive. Never tie the horse hard and fast during early sacking out sessions in case it pulls back; a slip tie or an experienced handler holding a long lead is safer. The rubbing motion should be rhythmic and progressive, pausing when the horse relaxes and resuming when it tenses — so the horse learns that relaxing makes the pressure stop. Introduce more alarming objects — tarps, slickers, plastic bags, flags — only after the horse accepts quiet contact from neutral objects without concern.