Shoo Fly boots worked great for my field boarded pony who lives in mud. However, they developed a bend near the top which caused the stiff portion to turn in, giving my horse sores that wouldn’t heal. He now has one thick scabby spot on one leg just below his knee. I don’t think I’ll be using them this summer, which is a shame.
I’ve also given up on fly sprays. He’d rather roll in dirt. I do use roll-on repellent to protect his ears and parts of his face. A fly mask will just be ripped off when playing.