Also want to add what happened with an old gelding I had. He was a reg. Tb and 16'3 weighing about 1,400lbs?? BIG guy. Whenever I would try to load him in the trailer, he would become a complete jerk and would try to run over me and push me over. I did the exact same thing as above. I knew for a fact he was fine with trailers so that wasn't the issue. It was all about respect.
I grabbed a lunge line and a while and did the exact same thing as posted above.
I would ask him ONCE to load and if he even started to think "no" then I would chase him and make him work SO HARD on the lunge line. It took me 30+ mins the first time before he understood that getting on the trailer when I asked him to was much more simple. By the end of it he was dead tired and realised I wasn't giving up. Never had problems after that. So good in fact I only needed to walk up to the ramp and he would finish loading by himself.
With these mind games, these smart horses it's not a question of over powering them or showing them who's boss but a matter of simply showing them that bad behavior means work. If they were smart enough to play games with you in the first place, they really very quickly learn that hard work isn't as much fun.
Another BIG key thing is to NEVER let something bad re-occur. Here are some examples with my own guy just over the last week alone.
When I lead him from the field to the barn, he's started to play and grab his own lead rope and he holds on to it all the way to the barn. He's only a baby and as much as I want to yell at him for doing that, I also know he's a baby and is probably going thru a baby punk phase so here is what I did....I went and got a stud chain. It's cold outside and just not fun to eat a freezing cold chain.Problem solved. No longer does that.
Today in the arena, he watched a 2 year old have a spaze attack and Cobalt ended up looking at the horse, no longer paying attention to me whatsoever. What did I do?....I halted him, back him up and halted him again. I waited 2-3 mins doing nothing making sure HE DID NOT MOVE a hair until I said he could. He did it and we went back to what we were doing.
Essentially I end up doing what it is they ddidn't want to do at least 2-3 times longer than how long it would have taken had it done it in the first place. If it's a horse that has to much energy and just doesn't care about your ground work, that's when the making them WORK HARD in the round pen kicks in. If they have the energy to be jerks, they will have the energy to work hard.