Learn what spooks him. I know my horse will react to bark across the road, the ends of hollow logs and wildlife so I make sure to see it before she does. If she goes passed/over the scary object calmly we coninue on our way but if she reacts I take her back, get off her and lead her up to it slow until she sniffs it and relaxes, then get back on and make her goes passed it a few times to consolidate. Another way is to work on getting your horse to trust you in the round yard/area over a similar (but safer thing) so the horse learns to respect your judgement of whats safe or not despite whatever their natural reaction is. My mare would freak out at crossing water so in the round yard I put down blue tarp and lead her cross it, then when she stopped avoiding it lunged her coss it, and finally (it was the hardest for her to do) made her stand on it without trying to shift off it. She now trusts my judgement on whether its safe to cross creeks even through the river bottom is uneven and she cant see it.

My other horse freaks out about flaps and noises on him like the sound of a drizabone flapping. To combat this sort of thing tell the horse to stand then make the noise and if they stay still (but tense) congradulate them then repeat that over and over gradually increasing the volume and duration of the scary sound until they relax. This also works with teaching a horse to let you crack whips whilst riding it.

Be sure to repeat the whole yard experience from start to finish either the next day or in a couple of days so the horse remember the new information (that the objest is not harmful).

He sopunds like my pony. She will happily follow a lead horse, but once asked to lead or go out alone she is a spooky huffy thing. This happens when they have to figure out things for themselves rather than letting a lead horse do all the problem solving.

You could try some natural horsemanship techniques to build a good groundwork bond and learn how to teach him to be calm in the face of new and weird things. The more odd stuff he sees and accepts, the better he will be able to deal with new stuff out and about.

Instead of trying to get my horse out on her own at first, I went out with others and then took turns leading, so my horse had a back-up group of horses behind her, but had to figure out that signs and bags weren't going to eat her. Then she would be rewarded by dropping back in line a bit. Doing this for a year has rewarded me with a horse who will happily lead out and who is ok with going out alone, albeit still huffy and edgy.

You'll need to take your time, and perhaps lead him out or lead him halfway so he slowly gets used to the great outdoors without horsey companions to rely on.

be calm and show him you're not worried, a horse can tell when you are nerous, he may be feeding off your nerves. if he is spooking when you go near him then just move slowly and show him you're not scary.

hope this helps xxx