In America today, an expanding network of surveillance cameras tracks our bank deposits, our shopping expeditions, and our workplace trysts in the supply closet. When we venture online, hundreds of companies diligently note the websites we consume, the files we download, and the comments we make. Our smartphones are even worse stool pigeons than our computers, constantly keeping tabs on our precise geographic coordinates. If you grow weary of such oppressive attention, if you long for a little Waldenesque solitude outside the crosshairs of our panoptic culture, there is still one place you can go to get away from it all: the borderlands of California, Arizona, New Mexico, and Texas.

That situation is ironic, of course. Long before Google Street View existed, long before we started sending out alerts every time we breached the perimeter of Starbucks, the U.S. government embarked on an epic quest to establish a "virtual" fence along the Mexican border. The year was 1997. And while the U.S. Border Patrol's surveillance technology then consisted primarily of sunglasses, border hawks and bureaucrats dreamed of a thin technological line of motion sensors, infrared cameras, and video-driven command centers producing the same sort of omniscience we now exert over 7-Eleven parking lots. To realize this bold but improbable vision, Congress approved funds for a pilot project called the Integrated Surveillance Intelligence System, or ISIS.

Thus began a long stretch of failure: cameras that wilted from the heat when thermometers hit a relatively temperate 70 degrees, ground sensors that could not tell a native cactus from an illegal intruder, inept project management, insinuations of fraud and corruption. Periodically, the quest would be canceled and then revived under a different brand name. ISIS begat America's Shield Initiative, which begat the Secure Border Initiative Network, or SBINet. In January 2011, Secretary of Homeland Security Janet Napolitano officially pulled the plug on this latest incarnation, thereby ushering in what arguably has been the project's most successful two-year run. Zero functionality was added during this time, but at least spending came to a standstill too.

Now the Department of Homeland Security (DHS) is ready to give the virtual fence still another go. According to the trade publication Defense News, U.S. Customs and Border Patrol (CBP), a division of DHS, has earmarked $91.8 million in its fiscal 2013 budget for the construction of what it calls "integrated fixed towers." In April 2012, CBP issued a request for proposal to build a single tower near Nogales, Arizona, and more than 100 companies, including Boeing, Lockheed Martin, Raytheon, and General Dynamics, expressed interest in pursuing the project. CBP was scheduled to choose a vendor in the fall of 2012.

If the federal government and its various contractors have learned anything during the last 15 years, it's that building a fence, especially a virtual one, over terrain that spans desolate mountains, wind-swept deserts, and meandering rivers, is no easy task. According to Robert Lee Maril, an East Carolina University sociologist who has written two books about the border, much of the equipment that was installed during the ISIS era is now "rotting in the West Texas wind." SBINet fared similarly. While initial plans called for a series of 1,800 towers deployed across the entire length of the southern border, Boeing, the project's primary contractor, built just 28 of them in a 53-mile section of Arizona, at a total cost of approximately $1 billion.

After these experiences, CBP is proceeding with the sort of plaintive foreboding more commonly seen in a gun-shy Match.com veteran than a major federal agency. "In all cases, CBP will seek strong confirmation that each offeror's system is truly non-developmental," its request for proposal advised. "Offerors must provide strong assurance that the proposed system is now ready, deployable and will not require additional engineering development if they hope to receive favorable consideration." Translation: It doesn't need all the latest bells and whistles. In fact, the agency will totally settle for a balding, nondescript, not particularly sexy surveillance system, just as long as it actually works.

The CBP (which was itself rebranded as part of DHS in 2003, uniting functions from two divisions of the Justice Department) wants to take things very slowly. If whatever vendor it chooses can deliver one tower whose associated cameras, radar, and sensors are capable of detecting a "single, walking, average-sized adult" within a range of 7.5 miles, and then transmitting this information in real time to a command post staffed by Border Patrol agents, then maybe, just maybe, it will think about building up to five more of them.

While CBP is terrified of another crushing disappointment, what is perhaps even scarier is the prospect of success. The agency's failure to construct a viable surveillance system has had at least one tactical advantage: It has kept people from questioning the value of a functional virtual fence. Any attention the project has attracted has focused mainly on diagnosing its immediate shortcomings rather than assessing its long-term utility as a means of deterring illegal immigration, drug smuggling, and terrorists seeking entrée to the U.S.

Building dozens of towers that don't really work as advertised has been somewhat costly, but how much would it cost if we had hundreds or even thousands of towers that do work as advertised? In the wake of 9/11, the Border Patrol has grown tremendously. In fiscal year 2000, it had 9,212 agents and an annual budget of $1 billion. Ten years later, the Border Patrol boasted 21,444 agents and a budget of $3.5 billion. A virtual fence, and the monitoring and maintenance it would require, will no doubt ensure a well-staffed, well-budgeted future for the CBP. But what impact would it have on the security of America?

"The main problem the Border Patrol faces isn't just seeing drugs or illegal aliens coming through," says Maril, the East Carolina University sociologist. "It's getting to wherever that's happening before the people are gone." While a more functional system may cut down on calls prompted by suspicious agaves, it won't help agents traverse harsh and often inaccessible terrain any faster. "You can't just get in a squad car and be there in 10 minutes," Maril notes.

In any case, there is no guarantee this iteration of a virtual fence will work any better than earlier ones. Tom Barry, a senior analyst at the Center for International Policy who focuses on border issues, notes that a retired Air Force major general testifying at a 2010 congressional hearing confessed that 12 out of 15 sensor activations are caused by wind. "They're spending many millions of dollars responding to weather events," Barry exclaims.

Yet the virtual fence continues to attract bipartisan support. The Obama administration has funded it for 2013. Mitt Romney's official campaign website promises to "complete a high-tech fence to enhance border security."

Such consensus derives at least partly from the virtual nature of the fence. In its earliest days, it was so ethereal, so magical, that its creators chose fantastical, almost child-like names to describe it (ISIS, America's Shield.) Now, after 15 years of costly growing pains, its latest moniker is the more pedestrian Arizona Border Technology Plan.

But even with the more utilitarian name and the new emphasis on humble pragmatism, longtime border watchers like Maril and Barry suggest that the ultimate costs and benefits of a virtual fence remain largely undefined, a hazy, constantly shifting mirage of heightened security glimmering in the farthest reaches of the Arizona desert.