The only other thing I would add is to look them dead in the eyes with a really nasty look when you do it. We call it the "mother-in-law" look. It's the same look the Alpha mare gives them right before she bites or kicks the snot out of them when they get in HER space. Before you know it, all it takes is "the look".
I've seen that look but I didn't know what it was called:')