background
barb
barbed
barbwire
barrier
black
border
boundary
confinement
convict
crime
danger
design
detain
enclose
enclosure
facility
fence
forces
freedom
guard
imprisoned
inmate
iron
jail
lockup
metal
patrol
penitentiary
power
prison
prisoner
protection
punishment
seamless
security
sharp
silhouette
steel
system
thief
wall
war
watch
watchtower
wire
wired