ache
barb
barbed
barbed wire
barbwire
base
border
boundary
camp
closeup
dangerous
defend
defense
entry
fence
forbid
forbidden
green
grey
guard
hard
invade
iron
isolated
limit
line
metal
military
obstacle
paint
pattern
prison
private
prohibit
property
protect
protection
punishment
razor
remain
remains
rust
rusty
sad
security
sharp
spot
steel
wire