Most residential “motion sensors” aren’t really detecting motion at all. PIR sensors detect very slight changes in heat, so they almost always fail in outdoor conditions. In fact, many manufacturers say they are for indoor use only for exactly this reason. Just a gust of wind can set them off if there’s a temperature differential.
Did you previously have WeMo sensors outdoors? (I’m assuming from your mentioning of leaves that your current sensors are outdoors.)
If your current sensors are outdoors, you might want to consider putting them into a zone where three or four have to set off at the same time before an event is counted. Mike Maxwell has a good smart app for doing exactly this. It might be worth taking a look at.