Ideas for natural product to protect hooves from rats?

We have a problem with barn rats and have taken all the natural measures to resolve it -- food in containers, cats, dogs, removing hiding places, snap traps, live traps, etc. I will not use bait so please don't suggest it -- too dangerous for the domestic animals. My mini horse's hooves are now the target of the evil barn rats. In a matter of days they managed to tear off hoof wall growth and nibble the frog down to the quick. (They are not going after the coronary band....this is the bottom of the hooves so it's being done when he lays down.) I have used iodine and wraps and now they've gone through that. My shoer has never seen this level of rat activity and only my mini horse is affected. Has anyone found a natural product that can be used to coat the hooves as a deterrent? I am going to try hot sauce tonight but if anyone has encountered this and has a solution, PLEASE help. After a week of iodine and wraps he at least wasn't sore, but that will change overnight at this rate.