“Ghost-catching marines” stationed a mere 1km away from forces of arch-rival North Korea are the first line of defence.
South Korean President Park Geun-hye has accepted the resignations of her top presidential aides, according to her office, amid a political crisis involving an old friend.
The friend, Choi Soon-sil, is the 60-year-old daughter of a South Korean religious leader and one-time mentor of Park.
Choi, who has close ties to Park but holds no official position and no security clearance, has been accused of abusing her personal connections for influence and interfering in state affairs.
Park carried out a partial reshuffle of her key aides on Sunday after ordering her secretariat to hand in their resignations earlier this week.
She accepted the resignations submitted by her chief of staff and four senior presidential secretaries, Jung Youn-Kuk, presidential spokesman, said in a statement.
Al Jazeera’s Harry Fawcett, reporting from Seoul, said Park has been facing calls to resign over the scandal.
“Park’s top aides stepped down after tens of thousands of protesters took to the streets in Seoul on Saturday to call for her resignation,” he said.
There were similar protests elsewhere, including the country’s second largest city, Busan.
Meanwhile, Choi has returned to South Korea to face revelations that Park discussed and sought advice on government policy from Choi.
Choi, who had been staying in Germany since early September, flew into Seoul on Sunday morning on a flight from London, according to her lawyer Lee Kyung-jae.
“Choi told me she will cooperate with the investigation and expressed her deep apology to the people for letting them down and causing them frustration,” Lee said.
As well as a public uproar over her relationship with, and apparent control over Park, she faces charges of using her links with Park to compel major companies such as Samsung into donating large sums to two non-profit foundations she set up.
Choi has spoken with prosecutors to schedule her questioning, Lee said.
The past week has seen a daily diet of increasingly sensational media reports regarding Choi.
Invoking a back-story of religious cults, shamanist rituals and corruption, the reports have portrayed Choi as a Rasputin-like figure whose influence extended to vetting presidential speeches and advising on key appointments and policy issues.
“As her attorney, I think the case must be thoroughly investigated and the truth be told to prevent any further eruption of speculation that goes beyond fantasy,” Lee said.
A public apology by Park, in which she acknowledged seeking limited advice from Choi, has done nothing to assuage public outrage over her behaviour or halt a plunge in her approval ratings to record lows.
Analysts say the scandal could paralyse Park’s administration, underling her lame-duck status in advance of presidential elections in December next year.
Choi is the daughter of the late Choi Tae-min, who married six times, had multiple pseudonyms and set up his own religious group known as the Church of Eternal Life.
Choi Tae-min befriended a traumatised Park after the 1974 assassination of her mother, who he said had appeared to him in a dream, asking him to help her daughter.
He became a long-time mentor to Park, who subsequently formed a close bond with Choi Soon-sil that endured after Choi Tae-min’s death in 1994.
Choi Soon-sil’s ex-husband served as a top aide to Park until her presidential election victory in 2012.