Our horse propety came with lots of small (6 inch diamater) trees on the pasture. Hopefully, they will provide cool shade for our horses, one day. If, that is, the ungrateful beasts don't strip them completely of the bark!! We have put thick plastic sleeves around the trunks, but the horses can still reach up to the lower branches. Any suggestions? Is there anything safe we can paint on the trees to discourage eating/stripping the bark from the trees?