arrest
barbed
barbwire
barrier
bars
behind
border
boundary
cell
chain
concentration
crime
danger
detail
felon
fence
forbidden
freedom
frontier
gaol
grid
guard
high
imprisonment
industrial
intruder
jail
justice
liberty
limit
metal
nobody
object
obstacle
penitentiary
prevent
prison
private
protection
razor
security
sharp
steel
structure
terror
texture
tower
urban
wire
zone