I just can't find it anymore. Someone wrote about making a plastic bottle spin on top of a tall stick by cutting flaps that catch the wind to scare off birds. We made one last year with the same principle but probably with more power.
Take one bottle, make a hole in the bottom just big enough to let the stick through. From four other bottles, cut the bottoms off about 5cm up from the bottom so you end up with four cups. Fasten these cups sideways half way up the bottle with wire so that all the hollow sides point the same direction. Put the stick trough the bottom all the way till it touches the top and push the other end of the stick in the soil. It'll spin like crazy with the slightest wind. -Ina
