abstract
background
barb
barbed
barbwire
barrier
blue
border
boundary
camp
close
danger
dangerous
defend
defense
detail
entry
fence
forbid
forbidden
freedom
guard
horizontal
industrial
iron
isolated
limit
line
metal
military
nature
no
old
pattern
prison
private
property
protect
protection
rust
rusty
security
sharp
sky
steel
trespassing
up
war
wire