If you go to Spain you will see all sorts of horses picketed along the expressways. They just put a halter, a long rope and drive a stake in the ground and leave the horse all day.. I approached a few and the pin in nothing but a big nail that anyone could pull out. Some horses have the rope wrapped around their legs, around their bodies but I never saw any of them fighting. Too bad anyone I talked too didn't speak English so I could ask questions.
My old endurance horse stakes out with a halter and long bungy cord without a problem
My last horse I staked out by ONE hind foot without a problem.. You can get collars for staking out.
At the ride I ran high lines for all the horse and never once had a problem. I would leave them enough lead line to touch the ground, even a nights.