You can teach a horse to ground tie in much the same way you teach a dog to stay. At least that's how I've done it. There's nothing wrong with ground tying, but I think it's ridiculous when horses don't tie. My horse does both. I've always used a strong lead and a rope halter, tied them to an immovable object, like a tree, until they yield. And ponied them with their lead tied to the saddle. I also have my horses run around in the pasture with their lead ropes dragging. They will step on it and then have to wait for me to come "fix" it.
However, if your horse is spooking, ground tying might result in him just taking off when he gets scared. Has he been sacked out? I think he should be introduced to all sorts of things, you should have him step on plastic bags, sewer drains on the street that make those lovely loud clangy sounds when walked on, get a whip and swoosh it around by him, have a friend sit in a car and rev the engine, honk, etc while you walk your horse by. It seems to me that he's just uncertain and inexperienced when it comes to the world around, so the more sights, sounds, smells, whatever you can introduce him to will help.
Also, why I prefer a good hard tree as opposed to something like a ring in the wall or a board is that the tree won't break, but if they break what they are tied to, it will just make another bad memory for them to hang on to. Best of luck! I hope you find something that works for you and your horse!