abstract
accessibility
background
barb
barbed wire
barrier
black
border
boundary
closed
concept
crime
danger
dangerous
dark
depression
despair
fence
forbidden
freedom
hopelessness
ideas
interdiction
iron
jail
keep
metal
ownership
prison
private
problem
prohibition
protect
protection
rust
sad
safe
safety
secure
security
sharp
steel
stop
stress
symbol
wall
war
warning