We have friends that sell concessions at a small threshing show during the summer. They put colored water in Zip Lock baggies and hang them from the corners of the door and windows of their stand. It works great when the sun is shining, but not so much on cloudy days or after dark.
I use permethrin. I also put permethrin poultry dust in the trays I have shavings, in my brooder and no flies. Every now and then I spray inside my coops and it also eliminate the flies in the coops. Some cow ear tags have permethrin in to help keep the flies away from the cattle. I have tried a lot of thing and this works best for me.