So my horse cannot handle flies at all. He's just come out of a show barn and is now a pasture horse so there are a ton more bugs than what he's used to. He's adjusting pretty well to all other aspects but the flies are killing him. He's coming out of his diva-ness but I really hate seeing him so stressed about something like flies. I'm not in a position where I could get a fly sheet on him every day, a mask maybe but his face isn't what bothers him. He's learning to be outdoors so he's getting loads more scraps and cuts than he normally would so flies are just swarming him. My farrier told me that oil based spray works better but people complain it makes the horse slick. I ride bareback currently so that isn't really a big deal to me, and I'd rather have him comfortable since I ride, at best, about an hour a day, so him being happy for the remainder is more important.
(The only reason his halter is on is because I was with him and was lunging him 5 minutes before, he's never out with it on)