I enjoyed these shelves by @GiskardReventlo but wanted to keep things from sliding off the back. In comes the rails that snap into the hex holes on the base of the shelf. I wanted a double wide shelf with a rail as well so created one in two pieces that snap together and then into the bases of two shelves next to each other. I didn't see the multi-shelf connectors by @deigge until I had already made my own but either should work to keep the shelves together.