I just found this thread, and read it all through.
First, I've managed facilities, and I've had my share of crazies that I've had to kick out...but *never* had anyone who even attempted to ride another person's horse. At one place, I did have a "loaner tack" section, if you will, and everyone was great about signing out and returning. Most times, it was returned cleaned better than when they borrowed. No one under the age of 16 was left unattended at either facility unless it was previously arranged.
I am so I very happy to see how this turned out, the crazies gone. I wish you, the Bo and other boarders the best of luck...and long term peace!
Secondly, I board my horses out with a wonderful private family. Our family has felt very blessed, having this board situation...but after reading this, it makes me so much more appreciative!!! Think I will be trying to figure out a way to show our appreciation!!!