Well, sounds like you're doing your part to catch him. Have you warned your friend about the guy? Is she going out to watch for him?
I'm assuming you bring a digital camera with you when you camp out for him, right?
I'd be sure to keep the horses in at night WITH a camera. I'd even set up my own battery powered cameras out where he usually lurks on the property. Those deerhunting ones that have a motion sensor are the best. Just make sure you have a high quality one that can get video/pictures in the dark cause it's worthless if you can't get a good look at the guy's face.
Anywho, I think I'd personally be freaking out a bit more than you seem to be.
You seem very calm and collected, lol. Which is fine. I would just be horribly offended that the guy had the nerve to go out and do that.
I'd also be QUIETLY spreading the word to your neighbors that they might want to think about setting up their own cameras. Remember that if the guy catches wind that he's being watched, he won't show up. That's good for you, but he might get bored and show up after a few months have passed, which isn't good. Better to be quiet and catch him in the act.