How to get rid of horse flys??

Question:have tried the water bags trick and fly-paper strips - nothing stops them, just keep getting more of them. is there a trick to get rid of them? there is no food or fruit around to attract them, but it doesn't matter to them. they have humans to eat up. HELP - thanks for your suggestions.

Answers:
there was a spray that we used on our horses you may be able to get at a vet supply or farm supply store, good luck, they are obnoxious pests!