Depending what you're doing, you can also arm yourself with a buggy whip
One of my three horses has been a bully all his life and tests everyone from me to the strong alpha-dominant horse. The Bully is third in line.
2 - 3 times a week he "accidentally" gets in my personal space when I am opening the paddock gate to let everyone in the main pasture.
If I were to always let that horse get in my space, it wouldn't be two weeks before he would be running me over to get thru the gate.
He is 16.1H and I am 5'2" - I can't be letting the Snot get away with anything. The buggy whip is my "arm" and while I'm opening the gate with one hand, he is getting poked in chest by my "arm" on the other side. If that doesn't grab his attention, I let him have it across the neck (never
in the face). He gets mad, snakes his head, starts chewing his tongue and waits until I tell him he can leave.
We've been doing this for 16+ years because he's a horse that will never quit trying me or the two horses who are ahead of him in leadership.
Horses don't stay broke and well-mannered by themselves - every time we're around them, they are learning something - either how to get one over on us, soon or later, or that they better be respectful