hang near your door a transparent plastic bag filled with some water, drop a couple of new pennies there. Through the eyes of the flies these pennies in the water look like formidable predators so they wont get near. 环保 无毒 and cheap google "penny in water hang near door" if you dont believe me.
环保 无毒的
https://www.amazon.com/Skeeter-Screen-Patio-Egg-Deterrent/dp/B076DMDY9S
买的时候注意，如果大门是铁门就无效，门帘会紧贴在门上，更加麻烦