Massive migrations have started for the Chuseok holiday season, as homeward-bound families hit the roads throughout the nation. Passenger cars are waiting in long lines to pass through the tollgates. It will take them two or three times as many hours as usual to reach their destinations.

Bus terminals and railway stations in urban centers are also crowded with homeward-bound people, many of them in colorful traditional dress. They will have to endure the ordeal of sitting on a bus or train for many hours.

But long hours of travel put no damper on the festive mood for those going home. Moreover, the three-day official Chuseok holiday, which starts on Saturday, is extended for many through the National Foundation Day on Wednesday.

Excluded from the festive mood, however, are Army troops patrolling the Demilitarized Zone, marines stationed in the northernmost islands and servicemen manning Navy patrol boats. Instead, they have been ordered to strengthen their guard against infiltrators from North Korea, as they invariably are during a holiday season.

During this Chuseok holiday, however, greater vigilance will be demanded of the armed forces stationed near the border with North Korea, in particular marines and Navy servicemen guarding the Northern Limit Line in the West Sea, the de facto maritime border with the North.

Tension at the maritime border has recently been heightened by frequent incursions into South Korean territorial waters by North Korean fishing boats. The South Korean security authorities regard the fishing boats, not as accidently running adrift into the South Korean waters while operating, but as intentionally violating the NLL in what they suspect is a prelude to unprovoked armed hostilities.

South Korea has grounds for such suspicions. North Korean fishing boats have crossed the NLL into the South Korean waters on seven occasions since Sept.12, ignoring warnings from South Korean patrol boats. On one occasion on Sept. 21, South Korean patrol boats fired warning shots to force the invading fishing boats back to the North.

North Korean fishing boats ignored the earlier warning and moved into the South Korean waters again on Tuesday, this time during the nighttime. The South Korean security authorities, which said nighttime incursions had been rare in the past, believe North Korea was testing the South’s defense posture. Moreover, they say they cannot rule out the possibility that military personnel were manning the fishing boats.

On Wednesday, President Lee Myung-bak called the defense minister, the director of national intelligence and other top security officers into session over the repeated incursions of North Korean fishing boats ― an indication that he took them very seriously. Lee and his security aides concluded that North Korea is considering rattling its saber ahead of the South Korean presidential election on Dec. 19 in a show that it is not regarding the NLL as the maritime border.

The NLL is a maritime demarcation line between South and North Korea in the West Sea, the line drawn by the U.N. Command for the defense of South Korea’s five northernmost islands when the Korean War ended in 1953. North Korea, which said in 1973 that it did not recognize the NLL as the legitimate demarcation line, declared an area containing the five South Korean islands as belonging to its territorial waters.

North Korea has since engaged in military provocations against the South in the area on numerous occasions, with the latest case being the bombardment of Yeongpyeong Island in 2010. The South Korean military authorities say that North Korea opened up some of its coastal guns and kept its patrol boats standing by each time North Korean fishing boats crossed the NLL into the South Korean waters.

South Korea, while beefing up its defenses on the island, have repeatedly warned the North not to launch a military conflict in the sea off its coast, saying that retaliation would be many times as harsh as its provocation. But the only way for the South to convince a skeptical North is to make good on its word the next time the North starts a military conflict.

Credence will be reinforced if Park Geun-hye of the ruling Saenuri Party, Moon Jae-in of the main opposition Democratic United Party and Ahn Cheol-soo, an independent, commit themselves to merciless retaliation against any military provocation from the North when they resume their presidential campaigns after Chuseok.