Hi Goat Man.A gift from me on the matter - Swap the locations of the colonies.This happens during the day when you're sure which colonies involved in the theft.
First year bee keeper here, and spent the afternoon getting first hand knowledge of robbing. My three small splits, with queen cells were looking poorly and we seem to be in a dearth. So I put in frame feeders. Activity increased greatly. I traced bees back to my other hives. I have added bent window screens which seems to have helped a lot , my question if you pull the tops , how long can you leave them off. And after you reinstall them doesn't the robbing start again?I've mentioned this before but haven't had the need to try it:
The state Apiarist in Maine suggested that if you have robbing occurring in your yard and are sure the culprits are your own bees, pull the covers completely off all the hives in the yard. It puts every hive, including the robbers, into a defensive posture.