Clean yard, clean horse, keep body surface temps cooler (fans, shade, inside day, out at night), strategically placed lights, I also rotate repellents but tend to only use them when a service is involved (vet, farrier, etc.): my guys spend a lot of time grooming each other and I am not big on them ingesting all that chemical …stuff.. Not a fan of fly sheets as I don’t see that they cover or protect the most bite-able parts and just make the horse hotter and more irritated. More sweat=more bugs.
I do feed Bug Check ( a garlic based supp) and find that tho the flies etc still hover and loom, they don’t seem to bite as much. Still looking for a GOOD tick deterrent (other than guinea hens and slathering pasterns and faces with pink SWAT… works GREAT! but looks funny..).
Sure there's right and wrong but mostly there's just a whole lotta different.