How to Desensitize a Horse
Desensitising teaches a horse to think rather than react when something frightening turns up. It also earns his trust — it proves to him you can guide him through a scare. We would all rather ride the arena or the trail without spooking and looking, and this is what builds that confidence.
Sensitising and desensitising
In round penning we moved the horse's feet and earned respect. That is a sensitising exercise — anything where we teach the horse to react to a cue by moving. Point in the air, expect him to lope that way. Step in front of his drive line, expect him to turn.
Sensitising is necessary, but it needs a counterweight. Do nothing else and you end up with a hot, nervous horse who is no fun to be around, anticipating and reacting when you did not ask. Moving his feet is all he has ever known, so he associates you and your tools with work.

Approach and retreat
Desensitising shows a horse he does not need to fear our tools or us, and that the right answer is to stand calm until he is asked for something.
It is pressure and release under another name: approach and retreat. You approach with the tool, and you retreat it when he calms and stops moving.
Start with the tools you already use — the lead rope and the training stick. Once he is calm with those, get creative. Plastic bags, feed sacks, anything that makes an odd noise or an odd movement. That is how you take it to the next level.
Desensitising teaches a horse to stay calm and trust you in every situation. It is no secret why it is one of the first things I do.
What you need: a halter and lead set — the feel and the weight are what carry the cue down the rope, which is why a heavy, stiff rope does this better than a soft one. The stiff four-knot halter and the 14 ft weighted lead are the same pieces sold separately.