Having a drill that you go through with scary situations helps both you and the horse cope. Don’t think too specifically about it what the scary thing is - though walking over strange surfaces would be a good idea , a “scary object” like a flag, a hula hoop, some aluminum cans in a feed bag, or just a plain old plastic bag could work just as well as long as they create at least a little bit of “wow, this is new” response. You are not trying to scare the horse out of his wits, just to help him go from the reacting side of his brain to engaging his curiousity.
I usually put the scary thing out in front of the horse, on the ground. If it is moving away from them, they generally will drop their nose and follow it. Once they have touched it a few times, I put it behind me but level with their shoulder and then do approach and retreat with it. Once they have gone through this drill with different things, it becomes a recognizable routine to them, and when you are on the trail, it gives both of you a familiar pattern to follow when addressing a strange situation - and you know your horse well enough to feel when to slow things down and when to apply a little pressure.
Or you can use a riding exercise that the horse knows well. For example, one day the sun was shining down by the river and the pods on the Scotch Broom were all popping open. This really set off my friend’s horse - who was very experienced on the trail - but none of the green horses. My theory about that is that he knew this was not normal, whereas to the others this was just another noise. Anyway, he was fritzing out, but she had nowhere to go, with horses in front and behind, and there was at least two hundred yards of this Scotch Broom to pass through, so she had him do shoulder-in. It didn’t alleviate his concern entirely, but it engaged his feet in a pattern that overrode his emotions enough to keep them manageable.
