So after my first bout with the robbing, I decided to build some robbing screens for my nucs to give them a shot. At night, I removed the sheets from my nucs and placed the robbing screens on, taping them into place with duct tape.
The next morning, I went out to check the bees, and sure enough I was able to catch the occasional bee coming out of the top of the robbing screen and returning to the main hive. I quickly checked the nuc and saw that it was still full of what I assume to be the "home" bees but even inside of the hive there was the occasional tussle where bees were biting the legs and wings of other bees in there. Fortunately the robbers had only had a few hours to work them over, and they seemed like they'd make it if I could stop the robbing.
I threw the sheets back over both nucs since that seemed to be the only thing that worked, and since both nucs have fairly new queens, I don't want to mess with them any more than necessary.
So my question is, why didn't the robbing screens work? My currently prevailing theory is that the mesh I used to make them was too "tight." I'd made the screens with some screening I had laying around, which is the kind you screen in a deck with, or make window/door screens. (I don't know enough to tell ya how many squares per inch they are.) When I went back to look at the robbing screens online, they're pretty much exclusively made with a mesh that's many times larger than what I used. I assume the mesh, being so tight, wouldn't have allowed the "scent" of the hive to draw the robbers to the wrong entrance?
Any ideas how to stop a hive that loves to rob? I'd prefer not to have to requeen since we're in a dearth, so that's probably a major factor, and the queen in the primary hive is an excellent layer with some super docile offspring.