Some people consider caltrops a political weapon in this era of wars for oil for vehicle fuel.
If you are such a person you should pursue your ends by peaceful means instead.
Remember Noam Chomsky's advice:
"If you fear the government the proper response is to get more involved in government, rather than less so, because the Government really is the institution that represents you."
Watch the movie "Weather Underground" to find out what some famous political vandals wish they'd done instead.
I think it was Bill Clinton who said, "It's best to conclude that bad policy is caused by ignorance, not malice."
Flying sharp metal will hit you in the eye.
If someone steps on one of these they'll get hurt.
Excellent photos by theinfonaut
Step 1: Nicaraguan Caltrop
These look like barbed wire barbs cut off and welded together, but they're much larger than any barbed wire I've seen. These were used in the revolution against Somoza in the late 70's. Nicaraguans threw them onto roads in front of troop truck convoys to delay them with flat tires.
Somoza was a ( yawn, yet another ) U.S. supported brutal dictator.
By the way, a recent issue of Time magazine reported that Nicaragua now has the lowest risk of terrorism in the hemisphere.