abstract
background
barb
barbed
barbwire
barrier
base
black
border
boundary
chain
closed
crime
danger
dangerous
edge
element
entry
fence
forbidden
frame
freedom
hard
industrial
invade
iron
isolation
jail
looped
metal
military
monochrome
nobody
old
pattern
prison
private
protection
razor
safety
security
sharp
silhouette
spiral
steel
trespassing
warning
white
wire
wired