Investigators from the U.S. Government Accountability Office (GAO) walked across unguarded border points from Mexico and Canada last year with simulated radioactive material to test the security of U.S. borders. Their findings were made public in a report late last year.

But experts weren’t particularly surprised. Col. Randall Larsen, USAF (Ret.), founding director of the Arlington, Virginia-based Institute for Homeland Security, called the report “like GAO telling me the sun rises in the East.” 

The notion of securing the 4,000-mile U.S.-Canada border is both financially prohibitive and practically impossible, says Larsen, who is also the author of Our Own Worst Enemy: Why Our Misguided Reactions to 9-11 Might be America's Greatest Threat.

Other experts say that even if we could secure the northern border, that would likely not prevent the type of attack on which the GAO based its investigation: detonation of a radioactive “dirty” bomb. Both Larsen and Kenneth N. Luongo, executive director of the Partnership for Global Security, which seeks to stop the international flow of nuclear materials, noted that al Qaeda manuals instruct operators to build weapons using materials found within the target country.

Radioactive materials like powdered cesium are common in American hospitals, for example. The U.S. Nuclear Regulatory Commission must do more to ensure that these dangerous materials are secure, says Luongo.

It makes sense to tackle the problem on all fronts, of course. Luongo notes that placement of passive radiation detectors at border crossings couldn’t hurt. But that’s a tall order. Larsen notes that in the state of Minnesota alone, 54 state roads cross the Canadian border without a U.S. Customs and Border Protection (CBP) presence.

The GAO’s tests were carried out in late 2006 and early 2007 and involved five separate border crossings, three in the north and two in the south. In their first crossing, GAO investigators met on opposite sides of the U.S.-Canadian border in plain view of private residences. The agent on the northern side carried a red duffel bag to his counterpart and returned to his vehicle. A resident alerted authorities and the CBP responded, but the GAO agent who retrieved the bag was gone.

A similar exercise was conducted in a different location within sight of CBP vehicles, but just out of view of security cameras. Authorities, apparently unaware of the crossing, did not respond. The GAO’s test of the southern border had a similar result.

Department of Homeland Security Secretary Michael Chertoff told Congress in his annual progress report that more than 18,300 border patrol agents would be deployed by the end of 2008—double the number since 2001. He noted that there were nearly 113 miles of fencing and 112 miles of vehicle barriers along the southern border.

That physical barrier is also being supplemented by ground-based radar, cameras, and unmanned aerial systems, the first 28 miles of which is called Project 28 in Arizona. (The full virtual fence project falls under the Secure Border Initiative and is called SBInet.)

The focus on the U.S.-Mexican border helps fight narcotics trafficking and illegal immigration, says Don Hamilton, executive director of the Memorial Institute for the Prevention of Terrorism in Oklahoma City. But the Canadian border poses a greater threat of terrorist entry.“Everyone I know who’s interested in terrorism is more concerned about Canada, because Canada has a large Muslim population. Mexico does not.” Hamilton says.

The CBP likely welcomed the GAO report in that it would bolster the case for continued funding of SBI. Congress has currently authorized $8 billion through 2013 for SBInet