The folks whose child I babysit keep four horses on our property at present. Adam has kept 'Tude here for many years, starting back when I still had Blue. 'Tude was Adam's first horse, his dream come true, you might say. Later, he purchased a mare, Sassy, which made three horses here, counting my own. Blue, gentle as he was, seemed to be the boss horse while he was alive, and the three animals got along well. 'Tude was always somewhat hard to catch, and he had a tendency to encourage Sassy to run away with him when his owner wanted to ride, but it was nothing Adam couldn't deal with. Blue always had a lazy streak and didn't bother running with the others.
These days the horse population changes frequently: Adam's wife is quite the cowgirl, and always has some horse or other in some stage of breaking or training. I can never keep up with the names of her animals because they come and go, but at present she has two mares here.
After Blue died, 'Tude took over as herd boss and decided he was a stallion. He does everything a stallion would do, short of actually impregnating a female. He is, evidently, what is known as a proud-cut gelding. He got even harder to catch, and worse about causing his herd to run when their owners came to tend them. He became absolutely phobic if he was separated from them in any way, to the point where Adam couldn't ride him away from the herd without him throwing a fit.
We have lately kept the horses out of the lot up by the house because we have had some close calls where they attempted to run out of the gate when it was opened for a tractor to pass through. Once, three horses actually did escape. There is nothing much more terrifying than having a herd of horses loose with a would-be stallion trying to keep them from being caught. We live near a fairly busy road; it was a horrible experience, one I never wish to repeat. After catching them, we decided to simply keep the gate to the lot shut, which kept them in the big pasture. However, the cows needed access to that lot in order to get to the barn to be milked.
Horses usually won't pass under anything that is lower than the height of their withers. So for several years, Cliff has fashioned a way for the gate to remain open wide enough for the cows to pass through, but with a barrier just below the height of a horse's withers, so they can't (or won't) enter.
Adam has recently become very frustrated with 'Tude's attitude (appropriate name, 'Tude) and decided the only remedy that would straighten him out... and also allow he and his wife to catch the other horses more easily... would be to start keeping 'Tude by himself. So he was moved into the small lot that horses are usually kept out of. We knew there would be no problem with him trying to escape alone, because his attention is always directed at the rest of the horses.
Isn't it great when everything works? But... (you knew there would be a but, right?)
One of the mares is pretty small, and she found out it was no problem to walk through the opening left at the pasture gate and spend time with her "stud"; she would stay with him until the others headed out to pasture, then she would join them. Cliff lowered the barrier. Even though her withers touched it, she still squeezed right through. Because that little filly is so small, she can hardly support 'Tude's weight when he "breeds" her when she's in heat. She's had some problems anyway, and his behaving this way every three weeks could compound those problems.
We can't really lower the barrier any more because Grace is a tall cow, and she needs to get through at milking time. We've talked about putting an electric fence at eye level with the filly, but that would make it hard for anyone to get through the gate with a tractor; you'd have to unhook it every time.
So what I'm doing now is keeping the gate all the way shut. At milking time I call up the cows, shoo away the horses that are loafing at the gate to be near 'Tude, and let the cows in. Now that we are all used to the routine, it seems to work: Tude is a gentleman, the cows get milked, and the other horses have the run of the pasture.
While we're talking about horse behavior, I should mention the other gelding on the place, Huck. He's a huge animal, I'm sure well over sixteen hands. One would think he would be the boss, but he is the meekest of the group. He's always getting kicked or bitten by the others, even by that tiny little escape-artist mare. He is at the bottom of the pecking order.