How do you get rid of horse flies in your house without poison or a fly swatter?

One thing that's helped with my horse is removing all the manure from his corral twice a day. Also, I noticed that the ground around his feeding area had been stomped down with layers of uneaten hay and droppings and water (even a little bit each day adds up). I hacked this back with a pickaxe and there were maggots in the ground. So, now I am vigilant about removing all organic matter every day to make the ground inhospitable to flies.