March 9, 2011: American commanders in Afghanistan are looking for a way to halt the smuggling (of goods and people) from Pakistan to Afghanistan. The problem is not the illegal movement of consumer goods and civilians, but the Taliban and Islamic terrorists who move back and forth, and use these "rat lines" to supply operations in Afghanistan (which, lacking access to the sea, means moving all goods overland). The latest idea to halt this unauthorized traffic is an old one; the use of electronic sensors.

This concept is half a century old. First tried during the Vietnam war, there was some success. Sensors (battery powered microphones and transmitters disguised as a bamboo plant or rock) were dropped from aircraft and then monitored. This was particularly successful along the "Ho Chi Minh Trail", a system of jungle trails and roads going from North Vietnam, through neutral Laos, south along the South Vietnam border, to Cambodia. This was how North Vietnam supplied its troops and local guerillas in South Vietnam, and the U.S. bombed it a lot. But the bombing tended to just blow up trees, not North Vietnamese. The sensors alerted American monitoring aircraft overhead as to where a convoy of porters (using bicycles) and trucks (along portions of the trail that had roads) was. Bombers were called in, and much damage was done. The sensors were also destroyed, and new ones had to be dropped. But here is where the sensor advocates encountered many of the problems with this seemingly simple and effective tactic. First of all, the enemy quickly figured out what was going on with the sensors. As well camouflaged as the sensors were, some were detected, and taken back north for examination. Troops were ordered to search for them, and in some cases bounties were offered. Convoys were made smaller, to limit damage. After a few years, the sensors were useful, but no longer a decisive weapon.

Fast forward to the last few years, when a similar sensor line was built along the U.S.-Mexican border. The professional smugglers quickly figured out how the sensors worked, and, by trial and error, came up with ways to disable the devices or get around them. Israel had a similar problem along its border with Gaza and the West Bank, but came up with a solution that would be too expensive for the Mexican border, and depended on the use of deadly force (remotely controlled machine-guns) that would be politically unacceptable along the Mexican border.

The Afghan-Pakistani border is much longer, and covers rougher terrain, than the ground in Israel and the Mexican border. That complicates the situation if you are using sensors, even if you can use deadly force. Moreover, on the Pakistani border, you have to worry about the sensor line being attacked from both sides, which makes the sensor solution more expensive, and vulnerable to attack. That said, it's still possible to use remote sensors for border security, but it would require using them in new ways (that are harder to detect and defeat.) This may be what the American commanders are thinking of, as this new generation of (smaller, more powerful and cheaper) sensors provides a lot of new capabilities that have not yet been put to the test in all possible combinations. But in the end, you have to keep in mind that the people trying to get through will usually be more resourceful and determined than you expected.