The clips that come with the parrot drone 2.0 are easy to loose and easy to break. However Parrot does not sell the clips separate from the propellers. Use these clips in lieu of E clips provided.
Place clip concave side down onto the top of the rod. While supporting the rod with your finders firmly press down on the clips until they snap in. It will be a snug fit, duh.
Make sure they aren't loose before you take flight!
I added updated clips (update 2a). They are a bit tighter and less likely to fly off. However after testing i would say the E-clips are best option but in a pinch these work fine. I wouldn't do any barrel rolls.