Where we use the really cheap & thin dollar store curtains they really flap. We too do them on the outside of the run. And we secure them with strapping. That minimizes the flapping. It does put holes in them. Which makes them last only one season.I got the 10 ply shower curtains. I installed them on the inside of the run EEEEk the wind got them flapping around the same day. I need to install them on the outside. The girls are spooked by them flapping in the wind.