Exactly. A Maginot Line from the Gulf to the Pacific topped with barbed wire, machine guns, searchlights, bottle rockets and scarecrows will be foolproof against a dozen Al-Qaida terrorists with a dirty nuke suitcase bomb. It's not like Al-Qaida has ever used ships or planes for their attacks, so a wall makes perfect sense.
I like your style. ;)
I'm not sure how a wall came into the discussion, but you're right - your way is much better, let's not do anything since the enemy can transport in a nuke anytime, if it hasn't already been done several times over.