I have worked a gelding threw this same problem.
I started by walking up to a tree just to see if there was a reaction. He was calm until I started to loop the lead rope around the tree, then he just freaked out, bugged eyed, and started pulling. As soon as he started pulling back, I started asking him to back up and back up and back up and back up.....you get the idea. Then we walked back to the tree. The more he fought the idea of standing by the tree, the more ground work we did. If he doesn't want to stand still, then MAKE him move.
Usually when a horse has that violent of a reaction to being tied, it's because something tramatic happened in that situation, and a horse has a memory like an elephant (forever and ever, amen.) The goal with working with your horse is to make being tied the "safe place" to be. Being tied means rest.
That gelding and I probably backed up 100 miles and did 200 miles of lunged circles (I am exaggerating here) next to that tree, but after a week or so, I could tie him to that tree and he was calm.
I wont candy coat it and exclude that the second day, he did spook at something (I don't think I will ever know what, his own tail maybe??) and he pulled and sat back on the halter. THANK goodness for Clinton Anderson's rope halter. (If you don't have one, go to Ebay
and find ebay store Flash's Equine Products, they sell halter/lead sets 1/2 price of CA for the EXACT same thing. I have tried a dozen other "just like the professionals" rope halters, and the Flash halters are the ONLY ones other than an actual CA that I recommend.) Anyways, he only pulled that one time, and he calmed himself down in a few seconds and stood TIED nicely.
Don't be afraid of a horse pulling back, it can be very scary, but every once in a while it's going to happen. That's why I invest in rope halters and yacht rope leads, so that the horse stays the safest when they are in "flight mode". Make sure you know the quick release knot!!!!
I have a 6 year old gelding that will stand tied to a leaf most days, but every once in a blue moon he rears up and sets back as hard as he can. Only he and God know why, the best I can figure is he's just hoping one of these days I will have forgotten to tie him and he can run off into the wild blue yonder... who knows?!?
I agree with the convenience of ground tying, but sometimes it isn't the most logical answer, like if you are going on a overnight trail ride with 200 other horses or to a show/rodeo/? Where you wont be standing next to the horse the whole time.
Good luck with your potential new horse! I believe as long as you are confident in your own abilities to handle a horse with an "issue", this problem can be resolved. If you are not confident, or decided he needs more help that what you can do, I would say you are a VERY smart person for doing a trail period! And move on to another horse. Just don't "over-horse" yourself! GOOD LUCK!