area
army
barb
barbed wire
barrage
barrier
border
boundary
captivity
cordon
crime
danger
defense
delimit
detention
deterrent
element
enclosure
fence
forbidden
forbidding
guard
hindrance
industrial
industry
insulation
iron
jail
limit
metal
military
outdoors
prison
privacy
private
property
protection
risk
row
safety
seclusion
secret
security
separation
sharp
spike
steel
system
thorn
trespass
warning
wire
zone