Being "herd bound" is a human term and a human problem.
Horses like being in a herd, as they feel safer. They feel safer in a herd because they have extra eyes and ears for danger. They also like companionship.
How long have you had this horse?
While it does take some time for horses to become friends, horses don't become "recently pushy and so herd-bound to the point they are dangerous" overnight.
How much experience do you have with horses? I suggest getting a horseman/"trainer" (they are different, but semantics for later) to help you.
Every time you work with a horse, you are either training them or untraining them. You can't step in the same river twice; you never work with the same horse twice. The longer you accept this behavior, the longer that he learns that it is okay to freak out.
Horses do best what they do most. You need to take him out alone more; once every now and then isn't good for the horse.
It is a process - not an event. Don't get greedy and try to fix it in one day. Once he relaxes for a few minutes, put him back (or bring the pony out).
You need to teach the him that he is safe with you - that you are the leader and that you know what's best. I'm not really a fan of the tie-up method. "Pucker up and suck it up, buttercup" isn't really the lessons/mentality I like to have when I work with a horse. Besides, that could backfire. If you hard-tie and he blows up, he could get injured. If you soft-tie and he gets loose, he learns a bad lesson; "I pull and I get release." Besides, tying traps a horse, which can make them freak out more.
Start slow, near, and steady. Don't start by taking him far, far away. Start within visible distance and work your way out.
Establish yourself. Ask him something and engage him - do not "punish" him. Ask him to back and/or lunge (or some other little "job") - something that controls his feet (Preventing movement is still controlling their movement, but it is, in my opinion, easier to make a horse move than trying to force them to stand.) - and gets his mind on you.
While your size could be a "problem", try not to make it one. You can see little miniature ponies bossing around large, tall drafts. Make him notice you - don't be a wall flower. Show him that it pays (well) to pay attention to you.
Last edited by Equilibrium; 04-17-2019 at 10:16 PM.