Fear of movement and noise is information, not defiance
A horse who spins at a flapping banner or startles at a dropped bucket is reacting to exactly the stimuli his instincts flag as a predator: sudden movement at the edge of vision and sharp, unexplained sound. Desensitisation does not argue with that instinct. It teaches, through many small experiences, that these particular sounds and movements predict nothing — the flapping thing has never once chased him, and the noise has never once hurt. That learning only happens while he is calm enough to notice the outcome, which is why the intensity of every step matters more than the number of repetitions.
Why flooding backfires
The old approach — tying a horse up next to a flapping tarp until he stops struggling — produces a horse who has shut down, not one who has understood. Flooding risks injury during the panic phase and often leaves the fear intact but suppressed, ready to reappear explosively under saddle on a road. Proper desensitisation keeps the horse below that panic threshold throughout: he is free to move away, his heart rate stays moderate, and he chooses to re-approach. The visible difference is a horse who looks, breathes out and relaxes, versus one who stands rigid and silent. Aim for the first picture every time.
Flapping objects: still, distant, then moving
Introduce a tarpaulin folded small and still on the ground at the far side of the school, and simply work around it doing familiar exercises, letting curiosity pull him closer over days. Then unfold it a little. Then let a corner move in the breeze. Then have a helper lift and lower one edge at a distance while you reward him for standing and looking. Flags, umbrellas and plastic bags follow the same ladder: stationary and far, stationary and nearer, gentle movement far away, gentle movement closer. If he rushes backwards or stops breathing at any rung, you have climbed too fast — return to the rung where he was bored and stay there longer.
Noises: quiet recordings paired with good things
Recorded sounds — applause, a starting gate bell, traffic, a dog barking — can be played from a phone at the lowest audible volume while the horse eats his feed, which builds a pleasant association at the same time. Raise the volume a notch only when the current level earns no more than an ear flick. Real-life noises are handled the same way: a helper drops a bucket softly at a distance, then normally, then closer. Avoid drilling several new sounds in one day; one sound, genuinely accepted, generalises surprisingly well to others.
Progress, regress and proof it in new places
Expect the occasional step backwards after a break or in a new location — a tarpaulin accepted in the home school is a new question at a showground. Plan short refresher steps in each new setting rather than assuming the lesson transfers whole, and keep notes on which stimuli he has accepted at which stage so helpers do not accidentally jump him three rungs. KinsLe's Care Teams supports that record: each stimulus and its current stage can be written into the duty for the day, and completed sessions are timestamped, so his desensitisation ladder is climbed one agreed rung at a time by everyone who works with him.