Last night's episode of CSI showed how a three-pronged garden trowel could be put to use in an awesome way--presumably in our case, as a defense weapon.
I may have also noted this before, but the ultimate shariken or throwing star is a sharp radial saw blade. The come in different sizes and some really ugly tooth patterns. If you are fanatical, the 11" blades even have promise as a shield against a knife attack. I see it in weilder one inch descending layers of smaller blades, with the biggest blade mounted flush onto a pied on plywood, a bit larger and squarer, maybe with a peephole or two. Imagine trying to maneuver your knife around the wielder of THAT.