Immigration and Korean Walls?

I haven't said much about immigration because (despite the fact that Americans are a minority among the researchers I work with) I haven't thought about it much. WaPo's Krautkammer argues for a wall along the border. I'm not opposed to a wall, but do have to call foul when he says this:

Can't be done? Israel's border fence has been extraordinarily successful in keeping out potential infiltrators who are far more determined than mere immigrants. Nor have very many North Koreans crossed into South Korea in the past 50 years.

Right. Now I don't want to give anyone bright ideas...but I'm pretty certain it's not the wall that keeps the Koreans apart, but the landmine fields. Please no one tell Lou Dobbs.