background

barb

barbed

barrier

black

border

boundary

brown

cage

close

danger

defense

detail

fence

forbidden

freedom

grid

guard

iron

light

line

link

mesh

metal

nature

net

old

orient

oriental

outdoor

perspective

prison

protect

protection

razor

rural

rust

rusty

secure

security

sepia

sharp

silhouette

sky

steel

sunset

texture

tone

wire

wired

yellow

zone