I don't really have much to add, except to really look into the Blocker Tie ring. One of the best gadgets invented since the safety stirrup, IMHO.
My first pony was also a real spook. I once was riding him in our big cow pasture, and my dad was at the gate, watching us. Dad opened a pop can about a quarter mile away, and in the time it took me to blink, my pony had done a full 180 to look at dad, snorting like someone had smacked him with a baseball bat. For 2 days after that I drank a lot of canned pop in the barn. Once he panicked because Mom was standing behind her car, bent over looking for something in the back seat. I can only assume he saw "bodyless feet" under the car. Fortunately that pony was a master of the spook in place, and I can count on one hand the number of times he ever covered ground in a spook. All that could really be done was get his attention back on me (moving his feet), let him get a good look at the scary thing in the moment, and then let him live in close proximity to scary things (once he spent a weekend with a folding chair in front of his stall) until the fear went away, or at least he was willing to follow my lead and focus. He was a darn good horse, he was just hyper-observant and reactive, and no problem once you expected it and planned for it.
Best of luck to you, I hope things work out!