"You can't fight markets," says David Shirk, associate professor of international relations and director of the Justice in Mexico project at the University of San Diego. "When a market reaches a certain size, you can't fight it."

Joe Garcia, a deputy special agent with the Department of Homeland Security and head of the San Diego Tunnel Task Force, would beg to differ. He and his colleagues have spent much of their careers doing just that, discovering more than 200 drug tunnels under the California-Mexico border since the inception of the task force in 1990.

"We want to make it so unattractive to do the type of work that they do, that they'll go somewhere else," says Garcia.

Garcia and his team are skilled at discovering tunnels and filling them up and have garnered favorable local press coverage on a number of big drug busts. But despite these high-visibility wins for Garcia's team, a recent report from the California Attorney General's office paints a picture of a California-Mexico border that's leakier than ever and reports that California has surpassed Texas as the nation's top methamphetamine entry point.

"For every mile of fencing we put up, for every extra thousand or ten thousand border patrol agents that we throw into the area, there's always some trafficker or some organization out there who's figuring out how to maneuver around those obstacles," says Shirk, who contributed to the Attorney General's report.

Garcia acknowledges that the team's initial approach felt a lot like "playing whack-a-mole," with a new tunnel popping up every time they shut an old one down. So, the team shifted its strategy and began targeting the heads of the organizations funding the tunnels, which reflects a broader shift in the U.S. war on drugs. Government efforts to systematically eliminate cartel leaders promptly destabilized the region and led to some of the worst bloodshed in the country's history.

"It was when the government decided to take on drug traffickers that the drug war became a literal war," says Shirk.

Decades of experience and improvements in technology have honed the tunnel task force's proficiency at detecting and eliminating tunnels, and Garcia's team has all but stamped out amateurish, unskilled smuggling operations. In this challenging environment, the most sophisticated and well-funded operations have cornered the market and see a bigger and better payout at the end of the proverbial, and literal, tunnel. As a result, the team has discovered numerous so-called "super tunnels" over the past five years: deep, multi-million dollar, professionally constructed tunnels boasting elevator shafts, high-powered ventilation, and even electric trains, possibly making them some of California's first ever profitable rail projects.

The technological arms race between law enforcement and drug traffickers has done little to shake Garcia's faith in the righteousness of his mission. He describes himself as the Dutch boy from the classic Hans Christian Andersen fairy tale, holding his finger in the leaky dike to hold back a flood until backup arrives with a more permanent solution.

"We know that's a long, hard road, and we may never be successful in our lifetimes. But we have to continue to lay that foundation down," he says.

That's one way to think about America's 40-year war on drugs. Another is to imagine a tiny tunnel underneath the border. You fill it. But another, bigger and better tunnel appears, so you assemble a special team of professionals to fill up tunnels and keep up with the professionals on the other side. And now, it's just you, and the professionals. You both learn and improve every time. The tunnels are getting bigger and better, but at least you're finding them. You are finding all of them, right?

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Approximately 6 minutes. Produced by Zach Weissmueller. Camera by Paul Detrick and Weissmueller. Music by Chris Zabriskie.