Hang them while camping etc. I'm not yanking any city or country boy chain's. We went from hundreds of flies to seeing the occasional one, but it does not hang around long.
Fill a Ziploc bag with water and 5 or 6 pennies and hang it in the problem area. In my case it was a particular window in my home. It had a slight but significant passage way for insects. Ever since I have done that, it has kept flies and wasps away. Some say, that wasps and flies mistake the bag for some sort of other insect nest and are threatened by this.
I swear by the plastic bag of water trick! I have them on the side porch of our house entry and all around the basement door. We saw these in Northeast Mo. at an Amish grocery store & have used them since. They say it works because a fly sees a reflection & won't come around.
Ziploc bags of water? My research found that each of the millions of molecules of water presents its own prism effect and given that flies have a lot of eyes, to them it's like a zillion disco balls reflecting light, colors and movement in a dizzying manner. When you figure that flies are basically prey for many other bugs, animals, birds, etc., they simply won't take the risk of being around that much perceived action.
FlyBeGone is an insecticide that works to create a fly-free zone for 7-10 feet in all directions. You are advised just to add clear water to FlyBeGone's specially formulated polymer bag and flies will soon disappear. It leaves the environment without unsightly dead bugs left behind or foul smelling poison released into the air.