Hunt for North Korea's 'hidden tunnels'
23 August 2012 Last updated at 00:45 BST
South Korea's so-called "tunnel-hunters" are a band of men who roam the countryside looking for signs of North Korean infiltration tunnels.
They say they are making up for the army's passive approach to the issue and believe they have found evidence of 17 tunnels so far.
The South Korean military is more sceptical, but four such tunnels have officially been found and sealed in past decades.
Shoemaker Lee Chang-gun is one of those who spends his free time searching for the tunnels along the two countries' heavily-armed frontier.
BBC News followed Mr Lee and his crew as they investigated a new find.