abstract
armed
army
background
barbed
barbwire
black
boundary
cage
choky
danger
deterrent
element
enclose
enclosure
fence
forces
frame
freedom
graphics
illustrations
iron
isolated
jail
keep
metal
nobody
out
outdoors
outline
part
pattern
power
prison
private
protected
protection
row
security
shape
sharp
spiked
steel
system
texture
thorn
wall
white
wire