Something you need to know is that a horse has two areas of concern that he wants to protect. The first is his juglar. He can see to protect that. The second is his hind legs only there's a blind spot back there. He will be more reactionary to the blind spot. When a horse is troubled by something ask him to move his hindquarters over a bit but keep him walking past. You are letting him protect his hindquarters and yet you are allowing him to better see the spooky object as you move away from it. While you are doing this keep your focus on something a hundred yards ahead so that the horse understands that that's where you are going, not to the spooky object. If you have to return that way he may not react at all as he's seeing it from a different side of his brain.