The strip of land dividing North and South Korea - the most heavily armed border in the world.
Tensions between the two countries are set to rise following an announcement by Seoul that South Korean soldiers can now shoot back if they come under attack.
Previously, the chiefs of staff were required to seek a response first.
Soldiers like Captain Kim Sang-min welcomed the new orders, saying their spirit was now stronger than ever.
In the past, South Korea and the US - its main diplomatic ally - have kept a lid on military action even when the South has been attacked.
But there are fears a small incident could escalate under the new orders.
As well as shelling an island in 2010 in which civilians were killed, North Korea is blamed for sinking a South Korean navy ship the same year killing 46 soldiers aboard.
On Wednesday a senior South Korean commander told lawmakers the country would launch a pre-emptive strike if a nuclear attack from the North looked likely.
South Korea warns of retaliation (1:08)
Feb. 7 - The South Korean military says it is ready to fire back immediately in response to an attack by the North. Sunita Rappai reports. ( Transcript )