I've been struggling with robbers all day today and read about how to construct a robber screen. However, Home Depot didn't have the size hardware cloth I needed and when I wandered hopelessly in the window department, I found a solution for those of us beekeepers who didn't get to take shop in High School.
I bought an adjustable window screen 10" high and 19" wide at its smallest. This is just a little too wide to serve the purpose, but I still had to create a new entrance for the bees to enter the hive.
From reading on Beesource, I believe the idea of the robber screen is to block the main hive entrance, thus keeping out the robbers who are attracted to the honey and to create a new higher up entrance for the resident bees who are attracted to the queen and will climb, crawl or whatever to get to her.
I used a piece of 1.5"x.75" board, cut to the height of the adjustable window screen. I hammered the piece to the back of the windown screen on both sides and then bungee corded the whole thing to the hive.
Here are pictures: http://beekeeperlinda.blogspot.com/2006/06/robber-screen-for-construction.html
I'll know tomorrow if this will thwart the robbers, but it looks like it fills the bill for a robber screen for the constructionallly challenged (like me)
Linda T in Atlanta