abstract
accessibility
background
barb
barbed
barbwire
barrier
black
blue
border
boundary
cage
closed
construction
crime
danger
defending
dividing
enclosed
enclosure
fence
forbidden
frame
freedom
guard
iron
jail
mesh
military
nobody
prison
private
protection
protective
safety
seamless
security
shape
sharp
silhouette
sky
steel
stockade
system
warning
wire
wired