I have to side with GingersHuman here. You already know what it's like to deal with an animal that you don't dare turn your back on; is that where you want to be for however many years this animal lives? Who else is at risk of harm from this horse?
http://www.aaep.org/info/horse-health?publication=703
http://www.aaep.org/info/horse-health?publication=703