@Huntin_Fool I totally agree you should not tie the horse with an unbreakable tie and let him “figure it out.” I feel like that would be setting up a situation where the horse might hurt itself or really panic and become traumatized about trailering at all.
Do you have anyone who can give you an assist with practicing loading? When I’m trying to teach a horse to load on my slant load, I use an assistant and I hand the lead rope out the window to them and tell them to hold it very gently, just enough to mentally cue the horse that they are being held by the person outside the window. I also have the assistant feed the horse some treats, not as a reward, but to get the horse to pay attention to the person at the window. I pat the horse and push them into their slant position before messing with the divider. And I go really slow about it, casually patting the horse and moving back and forth a little before going for the divider. Once the divider is closed, I go to the window and praise the horse and feed a treat myself, and I preserve this routine for a while with inexperienced horses so they anticipate me closing them in with me coming to their window with a treat.
If the horse starts going back, the handler lets the rope slide back through the window and we don’t try to stop the horse in any way. And we just start over, as many times as it takes for everyone to be totally bored and relaxed about it. I have never come across a horse that keeps backing off as some kind of a game, though I guess a horse could. But I usually trailer alone to meets so I value preserving a “no big deal” attitude about loading.