Hello! I have experienced the attitude of “No-way-am-I-keeping-this-thing-on!” from my horse too (although we don’t struggle with sunburn). I would go out to my barn, turn my horse out with a fly mask, then come back three days later, and it was off. It happened time after time again. My recommendation it that you find a different fly mask, either a different model from Cashel, or a different brand. You could possibly try to find a different size. Also make sure that the Velcro is tightened as much as possible.