abstract
access
background
barbs
barrier
boundary
captivity
cloud
coil
concept
crime
cross
danger
dangerous
defense
detention
enclose
enclosed
enclosure
escape
fence
freedom
galvanized
gray
imprisoned
iron
jail
mesh
metal
military
obstacle
perimeter
prevent
prevention
prison
privacy
private
protect
protection
razor
safety
secure
security
sharp
sky
steel
twisted
war
wire
zone