Uh first of all that wall is meant to keep people in. Starving North Koreans under the yoke of some meglomaniac, whose is loved by Madeline Albright, would love to get out.
Also how long is the wall that seperates the Koreas, 100 miles. Probably at a minimum takes 3-5 billion doolars to maintain yearly, Multiply that number by 20 and you get a cost of $100 Billion yearly for your wall on the Mexican border.