abstract
army
background
barb
barbed
barbwire
barrier
border
boundary
camp
captivity
concentration
construction
contain
cordon
crime
cross
danger
design
farm
fence
forces
frame
freedom
gate
guarded
illustration
imprisonment
isolation
jail
keep
keep out
locked
pattern
prison
protection
secure
security
sharp
silhouette
steel
sting
sun
sunset
texture
trespass
war
wire
zone