Years ago, I started seeing transparent plastic bags full of water hanging in the doorways in my hometown, the given reason being that they prevented flies entering the bar or the house.

I thought that was some kind of joke, but... it seemed to work, at least when the bags were under direct sunshine. Flies weren't very happy flying in the vicinity.

Later people, emboldened, decided that strings of discarded CDs keep pidgeons away from balconies. I can't attest to that.