"We take our job very seriously," says Phil Stanford, chief inspector for passenger operations. "It's not like it used to be."
Among the improvements: every truck crossing the border is X-rayed.
But, as CBS News Correspondent John Blackstone reports, just half a mile away the border all but disappears.
Between the official ports of entry, vast stretches of the border with Canada are unfenced and wide open. Near Lynden, Wash., Boundary Road is in the United States, while Zero Avenue is in Canada. This international border is decidedly low key.
It's one of the holes in security the border patrol has tried to close since Sept. 11. Now high- powered cameras scan for intruders.
But what they see most often are drug runners throwing bags of marijuana across the border. The border patrol has caught plenty of smugglers but so far no terrorists.
"Every day is a challenge," says Joe Giuliano, who runs western Washington's border patrol detachment.
A fence would alleviate the problem, says Giuliano, "but quite simply a fence is an unacceptable alternative to this issue."
But with a huge population of recent immigrants from the Middle East and Asia, and a famously liberal immigration policy, Canada has proven an easy place for terrorists to get in, fit in and hide out.
"We know that in British Columbia that there are terrorist cells that are located close to the border here," says Debbie Engels, of the Bureau of Customs and Border Protection.
Canadian authorities last month arrested 19 Pakistanis rumored to have terrorist ties. And the FBI has just issued an alert for Abderrouf Jdey, a suspected suicide terrorist who holds two Canadian passports.
Four years ago in Port Angeles, Wash., Diana Dean was inspecting cars coming off a ferry from Canada. Something about Ahmed Ressam made her suspicious.
"It was just chilling," she says. "It was like time stood still.
"You're just looking into somebody's eyes trying to find an answer."
Ressam's trunk was loaded with explosives. He's now in prison for plotting to blow up the Los Angeles airport.
"The unfortunate reality is that we have no 100 percent guarantees about the border," says Deborah Meyers, of the Migration Policy Institute.
Meyers studied security on the Canadian border since Sept. 11. Despite improvements, she says, it's a work in progress.
"There's no end of the tunnel where we reach it and we're done," she says. "This is going to be a continuous ongoing effort."
That means looking for new and better ways to defend the world's longest undefended border.