abstract
background
barb
barbed
barbwire
barrier
black
blue
border
boundary
building
camp
catch ed
chain
cloud
concentration
danger
day
drainpipe
fence
forbidden
freedom
guard
iron
jail
light
lightbulb
line
metal
military
old
outdoor
prison
private
protect
protection
rampart
razor
razor wire
roof
safety
security
sharp
silhouette
sky
steel
was
white
wire