Much of this dusty city along the border is separated from Mexico by a fence consisting of 12-foot vertical metal bars, spaced inches apart to prevent illegal immigrants from squeezing through.
Surveillance cameras are mounted on towers nearby, and Border Patrol agents posted hundreds of feet away in the desert scrub and flowering ocotillo watch for anyone who might try to scale, cut through, slip under or sneak around the fence.
Though these fences are criticized for shifting would-be border-crossers to more dangerous and remote spots, they do make it harder for illegal immigrants to reach urban areas where they can slip into a car and head for the nation's interior to find work.
Now, as Washington seeks to overhaul America's broken immigration policies, Congress is considering putting many more such barriers along the 2,000-mile U.S.-Mexico border, which already has 83 miles of fences.
A bill that cleared the House in December would put fences at immigrant- and drug-smuggling corridors in all four southern border states. At an estimated cost of $2.5 billion, the fences would cover 850 miles of border - roughly one-fifth the length of the Great Wall of China - though it would not be one continuous wall.
The gaps would be policed the way many remote areas of the border are already guarded now: with motion sensors, cameras, unmanned drone aircraft and Border Patrol agents.
Among other things, House legislation calls for a mostly continuous 392-mile fence from Calexico, Calif., to Douglas. The second-largest piece would be a largely uninterrupted 305-mile segment in the Texas brush country from Laredo to Brownsville, a corridor used by cocaine smugglers.
Immigrant rights groups say fences waste taxpayer money because would-be border-crossers who are desperate to earn a better living in America will always find a way around or through barriers, as evidenced by the lower sections of the fence in Douglas, where rods have had to be welded into place to patch up breaches.
Even some proponents say erecting fences, without using other border enforcement efforts, will not stop illegal immigrants.
"All by itself, it's not a magic solution," said Ira Mehlman, spokesman for the Federation for American Immigration Reform, which favors limiting immigration.
But the Border Patrol says fences slow down immigrants so authorities can have enough time to respond to those who try to come across. That, in turn, frees up other agents to focus on remote areas, where they already use aircraft and ground sensors.
"Fencing by itself is not effective, but not having a fence is not effective either," added Sen. Jon Kyl, R-Ariz.
Advocates for beefing up border security said a 14-mile fence near San Diego, once the country's most prolific smuggling center, shows that barriers work. The fence there is made of corrugated metal sheets previously used as landing surfaces for military aircraft. Behind it is a second fence, made of tightly woven mesh.
Within that area, the barrier is credited with dramatically reducing the flow of illegal immigrants.
Rep. Duncan Hunter, a California Republican who is the leading voice in Congress for more fences, said the costs of building fences are much lower than the government expenses associated with illegal immigration, including huge sums spent on incarcerating immigrants convicted of crimes in the United States.
Opponents say there are some costly consequences as well. Immigrant rights advocates say fences prompt migrants to cross in remote areas where they face dangerous obstacles, such as rivers where some drown, deserts where some succumb to the heat, and mountains where some are injured or die.
Also, a large-scale fence could force immigrants to remain in the country longer, while in the past they came to earn money and then returned home, said Angela Kelley, deputy director of the pro-immigrant National Immigration Forum.
"If it's riskier and harder, people don't leave," said Kelley, who believes a guest worker program will reduce illegal crossings.