The propane thingy works great for mosquitoes, but is kinda expensive if I remember right, about $100 or so but the propane tank lasts a long time like spiffy said, and it definitely works on mosquitos but not so much on flies.
I smoke on the back patio when the weather is good and if my wife is sitting with me she always lights up the chiminea and smokes the place up with pinion pine....this seems to keep the flies away.
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