We have caltrops here, is a weapon made up of two (or more) sharp nails or spines arranged in such a manner that one of them always points upward from a stable base. Caltrops serve to slow down the advance of human troops and the like such as unwanted people, and wheeled vehicles with pneumatic tires.
Look like this: Cost about $3 to $5 bucks a pop. Or you can make them cheaper.
http://img178.imageshack.us/img178/1...caltropio9.jpg
I got six from my department, love them though never had to use them.