Maybe add single-speed gearing too? Then the would-be thief will have to be in good shape to get the bike moving... and be in better shape to stop it.

As for gears, I'm pretty sure some CNC shops can easily stamp those out for you if you supply them with a CAD file... although I've not messed with AutoCAD in a while, it shouldn't be too hard to spec out what type of gears you are desiring.