abstract
background
barbed
barrier
black
border
cage
chain
chain link
chained
construction
danger
design
detain
drawing
element
enclose
enclosure
fence
forbidden
graphic
grid
illustration
industrial
industry
iron
isolated
jail
link
linkage
mesh
metal
metallic
net
pattern
prison
protection
safety
seamless
security
shape
silhouette
steel
texture
urban
wall
white
wire
wired