Theres a horse at camp, Saturn who will step on your foot and then not budge. It usually happens when campers are cantering and someone is waiting with the line (they canter one at a time as they're mostly newbies, a staff waits with the line up of horses waiting to canter just in case) I've had camper pulling on the oppisate reign kick and clucking while I push on him. Never moved an inch. I figured out to punch him in the neck, not hard just enough force to say "ow! Get of my foot you stupid lovable pony!!"
And a few other times by other horses but for the most part they move off right away.
Equestrianism; 10% luck, 20% skill, 15% concentrated power of will, 5% pleasure, 50% pain and 100% reason to remember you're absolutely insane to be riding a beast that big.