When I said "ensuring smuggling is not going on", I freely admit I chose the words carelessly. It is not a binary matter (it happens or not), but a quantitive one (how much does it happen).

So while Keith is right that 'some smuggling' has always gone on across that border, what matters is the amount, not whether it does.   And standard security analysis says if you want more control you have to harden the border, but if you are willing to accept a greater degree of cross border crime, you can soften it.