abstract
background
barb
barbed
barbwire
barrier
black
blue
border
boundary
cage
chain
chained
chainlink
danger
design
element
enclose
enclosure
fence
fences
forbidden
freedom
grid
guard
industry
iron
jail
linkage
mesh
metal
military
prison
protect
protection
railings
razor
safety
security
shape
sharp
sky
steel
system
texture
wall
wire
wire fences
wired