The longest undefended border in the world?

I found a little piece of news today - apparently, the US House of Representatives has passed a bill calling for a security fence on their border with Mexico, and another on the northern Canadian border. If the Senate and the President ratified that bill without removing that provision, we would no longer have the longest undefended border in the world, as there'd be a fence across it. It won't likely pass, but its worth watching.