You have to be pretty darn paranoid to put antiaircraft guns on prison camps to prevent rescue in acountry that doesn't have any aircraft outside of government hands.
I hear that North Korea actually rakes its beaches- all of their coast, every day, to make sure that no one can cross the beaches into North Korea from the sea without leaving footprints. They are that nuts... makes our INS look really lame.
They rake the South Korean beaches too, to guard against the very real threat of N Korean agents, terrorists and sabateurs landing.