I have made racks that utilized locking pins. What I did, since melamine is .75" thick was drill holes (1/8" or 3/16", whatever the OD of the pins) about 1/2" into the bottom front of the shelves. I used two pins per bin with 1.5" steel pins. When the bin is in the shelf, the pins are pushed into the holes so the bin can't be pulled out without first pulling the pins out. You can also use sections of wood dowels as pins.