abstract
authority
background
barb
barbed
barbwire
barrier
black
blue
border
boundary
camp
chain
concrete
confine
confinement
construction
crime
cut
danger
design
edge
fence
forbidden
freedom
gaol
guard
imprisonment
industrial
industry
iron
isolated
jail
metal
military
penitentiary
prison
protection
razor
refugees
safety
security
sharp
sign
sky
steel
trapped
wall
warning
wire