Simulated barbed wire or razor wire- designed to fit any scale from 15mm (1/100) to 54mm (1.35).
Cut the desired length with clippers or pliers.
Wind it around a rod of appropiate diameter according to the scale needed, to make coiled reels of barbed wire.
String between posts to make barbed wire entaglements; you can use bits of cocktail sticks or matchsticks for wooden posts, or bent wire metal posts.
As an approximate guide, waist-high post should be about half of the height of a figure in the scale you are using.