abstract
background
barb
barbed
barbwire
barrier
black
border
boundary
conflict
construction
danger
dangerous
design
fence
fighting
foreground
freedom
horizontal
iron
isolated
jail
metal
military
nature
outdoors
prison
prisoner
private
protection
rust
safety
security
shape
sharp
silhouette
sky
spikes
steel
sunset
symbol
system
texture
thorn
trespass
war
warfare
warning
white
wire