I think its a pretty large leap of faith to think he's even in Iraq. I suspect he is still in Syria.
I'm also not convinced border gaurds are going to make one iota of difference in a place where you can walk across a border un-hindered. God knows they haven't done a bit of good on the Mexican border.
When he says Zarqawi, already being sqeezed in Iraq, I suspect he more then Zarqawi himself means his network and that after Iraq is stabilized he will have to move his fighters from Iraq elsewhere to create a new base of operations.