abstract
background
barb
barbed
barbed wire
barricade
barrier
black
border
boundary
chain
clouds
cloudscape
crime
criminal
danger
dangerous
dark
fence
forbidden
freedom
gaol
horizontal
iron
jail
law
link
mesh
metal
military
moody
orange
outdoors
post
prison
private
property
protect
protection
protective
razor
safety
secure
security
sharp
silhouette
sky
steel
stormy
wire