I would gladly settle for one as relatively non-porous as that between North and South Korea. There are damned few picnickers, cigarette smugglers or economic refugees crossing the minefields and impact areas thereabouts.
Actually, North Korean special forces infiltrate South Korea on a very regular basis. And I won't even touch whether or not the South Koreans return the favor. And the Korean border is only 154 miles long. It is one of the most heavily guarded and patrolled borders in world history. And remains unsealed. If we want to get anything even close to what they have along our 1700 mile southern border, you better be ready to sell the house, because everything you own will be converted to Federal tax money. And the border still won't be sealed.