abstract
barb
barbed
barbwire
barrier
black
blue
border
boundary
chain
construction
danger
dangerous
defense
design
fence
field
forbidden
frame
freedom
graphic
guard
iron
isolated
isolation
jail
metal
object
outdoor
pattern
people
prison
private
protection
rusty
safety
secure
security
shape
sharp
sign
silhouette
sky
steel
symbol
system
war
white
wire