This has worked for me for the past 12 years :
TURN OUT
And lots of it.
In huge huge open fields, where most horses go out for the first time and say “Oh my GAWD where’s the fence?”
(seriously, so many horses are stabled in small paddocks, it is no wonder they get a little agorophobic in the field).
Then I start to leave them out overnight. After a summer of wildlife tramping through the fields, all sorts of noises, and plenty of places to gallop to, they pretty much calm down.
Then I start leaving each horse out alone (sorry, my pet peeve is herd-bound horses. I absolutely cannot STAND to have a horse worry at the gate or pace the fenceline when you take away his buddy. All my youngsters have learned how to tolerate being alone, and hey, when there is all that grass to eat, who cares about a buddy).
PLAY WITH THEM ON THE GROUND
No . . not Parelli.
But be in a safe place and get your horse used to using his “thinking brain” instead of his “reacting brain”. I have found this is easier on the ground than in the saddle. Once you have thrown everything at them for a few months, you can try this riding.
I put all sorts of obstacles in the arena, tarps, plastic bags, a mailbox on a post. Things your horse will come across in the real world. How can you expect your horse to be calm around these things on a trail ride when he cannot experience them on his relaxed “home turf”?
(Oh, but don’t try putting carrots in the Big Scary mailbox to help bombproof them. I have one gelding that will drag you off the rode to molest black mailboxes. He swears it is a carrot-feeding-box and has to check each one out. Can’t rightly explain to the neighbors why there are horse teeth-marks on their mailboxes!)
Flap tarps, set free whispy plastic grocery bags. Enlist friends to bring over strange dogs. Have kids ride motor scooters around the outside of the arena.
Anything you can think of. I take down people’s election signs that they had in their yard (after the elections, duh) as one of my horses just HATES those little colorful plaques that get poked in to the ground.
Somedays I mix it up and put these things out in the pasture. A pile of tires in the corner of the arena becomes boring after a week or two, but when you put the exact same tires in the pasture . . well, that’s something new to spook at.
You just have to keep “setting” your horse up, not to “Fail” and to spook, but to be ALLOWED to react. Over time, the reactions get smaller and smaller. And you can learn to judge each individual horse. Does he rear when he is scared, jig, turn a whirl? It is nice to know this BEFORE you get him out on the trail. . .
I know people who just take their horses out and expect to learn as they go. I’m too much of a coward for that. Too much can happen in the real world if you discover your horse it totally phobic of trash. I’d rather do it in an enclosed arena with other people around.