architecture
background
ban
barbwire
barrier
blue
boarder
border
boundary
building
danger
disallow
fence
forbid
free
freedom
frontier
gaol
guard
hazard
imprisonment
jail
jeopardy
lesson
menace
military
outlaw
peril
prison
prohibit
proscribe
protect
protection
razor
risk
safety
security
sky
steel
threat
tower
turret
view
wire