Of course, unmanned aerial vehicles, cameras, poles and sensors cannot bar illegal immigrants from entering U.S. territory. They may be able to fly over, videotape, inanimately stand by or passively sense illegal immigrants, but they cannot stop them.

Even if every U.S. Border Patrolman were equipped with a Jack Bauer-type handheld video receiver that pointed out for him in real time the "virtual" image of every illegal intruder attempting to cross his sector of border, it would still be up to the Patrolman to physically stop those intruders.

In the real world, some of those intruders would be bad people capable of inflicting real harm.

A virtual fence is specifically designed to force hands-on confrontations between Border Patrolmen and foreign nationals crossing our border. It would cause dangerous situations, where a real fence could deter and prevent them.

If your son were a Border Patrolman assigned to watch a remote section of border in the wee hours, what would you rather have standing between him and a group of intruders: a high double fence with a patrol road? Or a motion detector and camera?

A real fence would create both a barrier and deterrent to illegal immigrants. Low-tech as it might be, it would be a far more discriminating and proportionate instrument for defending our border than a high-tech "virtual fence."

Many politicians of both parties eagerly point out that most of the illegal aliens in the United States came here seeking a good job and a better life. This is surely true. But many of the same politicians, including Specter, just as eagerly insist that they want to secure our border against future waves of illegal aliens.

There is a bipartisan consensus, in other words, that the U.S. border shimmers in the desert as an attractive hazard for those who would cross it illegally. In this way, it is like a community swimming pool that the city fathers never bothered to fence.

If people kept drowning in an unfenced pool in your town -- because they tried to swim illegally when the lifeguards weren't there -- which politicians would you believe really wanted to secure the pool: the ones who said they would build a fence? Or the ones who said they would buy an unmanned aerial vehicle to fly over the pool with a video camera?

The House has approved 700 miles of fence for our nearly 2,000-mile southern border. That, at least, would be a good start.