access
army
background
barb
barbed
barbwire
barrier
blue
border
boundary
closed
crime
criminal
danger
dangerous
day
defense
escape
fence
forbidden
freedom
frontier
grid
guard
human
industrial
jail
liberty
limit
metal
military
prevent
prison
private
protection
rights
safety
security
sharp
sky
spikes
spiral
state
steel
terror
violence
wall
war
wire
zone