North Korea's move to build a wall along the military demarcation line: what is its possible purpose besides emphasizing ”anti-unification”?

It has been revealed that North Korea is proceeding with the construction of a wall along the military demarcation line with South Korea. The South Korean newspaper Chosun Ilbo reported, "North Korean Chairman Kim Jung Eun announced at the end of last year that all members of the Workers' Party of Korea will be democratized.