abstract
arrest
barb
barbed
barbed wire
barbwire
barrier
black
border
boundary
camp
closed
cloud
crime
danger
dangerous
defense
enclosed
enclosure
escape
fence
forbidden
freedom
guard
iron
jail
liberty
metal
military
prevent
prison
private
property
protection
runaway
rusty
safety
secure
security
sharp
sign
silhouette
sky
spike
steel
symbol
war
white
wire