accessibility
army
barbed
barbwire
barrier
border
broken
cage
camp
closed
clusters
concentration
concept
crime
danger
dangerous
defense
dull
escape
fence
freedom
frontier
gloomy
gray
hole
imprisonment
iron
jail
metal
military
nobody
obstruction
outdoors
prison
protection
protective
safety
sea
seashore
secure
security
sharp
sky
spikes
thorns
wall
war
warning
water
wire