As President Donald Trump begins the work of transforming his “Build That Wall” campaign chant into reality, he won’t be facing a blank canvas.

The United States has a hodgepodge of barriers along the Mexican border totaling some 650 miles. They include pedestrian fencing, vehicle barriers, and double-layered steel fencing with enough space for border agents in vehicles to patrol.

“We’re not reinventing the wheel. We already have fencing. We’ve been through this before.”

On the campaign trail, Trump frequently spoke of a “big, beautiful wall,” but experts contend that the final product likely will not be one solid wall stretching hundreds of miles. Trump himself said in a “60 Minutes” interview shortly after the election that fencing would be appropriate in certain areas.

Brandon Judd, president of the National Border Patrol Council, said officials already have started the process of determining which barriers need to be strengthened, which need to be replaced, and where new construction on currently virgin territory needs to take place.

“We’re not reinventing the wheel,” he said. “We already have fencing. We’ve been through this before.”

Jessica Vaughan, director of policy studies at the Center for Immigration Studies, said barriers are not feasible or necessary in remote areas, mountainous regions, and parts of the border where water separates the countries.

“It’s not going to be a coast-to-coast wall or fencing, even,” she said.

[lz_graphiq id=ldGuAhAplPv]

The San Diego Experience
In planning the massive construction project, the experience in San Diego might prove instructive. At one time, the 66-mile section of the border extending east from the Pacific Ocean was the most popular entry point for illegal immigrants from Mexico. Migrants freely crossed from a region of more than 2 million people in Tijuana, Tecate, and surrounding areas.

In 1993, America completed the first 14 miles of fencing. The 10-foot-high fence was made from surplus Army steel landing mat used to make landing strips during the Vietnam War. Later, the United States added a secondary fence behind the first barrier. The two-piece barrier angles toward the south to make it more difficult to scale.

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The results were stunning. In fiscal year 1992, border patrol agents had apprehended 202,173 people at the border agency’s Imperial Beach Station in San Diego and 158,952 at the Chula Vista Station about 12 miles east. A Congressional Research Service report indicates that by fiscal year 2004, apprehensions dropped to 9,122 at Imperial Beach and 9,923 in Chula Vista. Those were declines of 95 percent and 94 percent, respectively.

In the rest of the San Diego Sector, apprehensions dropped from 204,456 to 119,293 over that time period.

Those regions also experienced a marked drop in crime, while crime declines in the more rural sections of the border lagged behind the national average, according to the congressional report.

“I’ve seen how effective [fencing] is in California and west Texas,” Vaughan said.

Yet for all of its success in blocking illegal immigrants from entering San Diego, there is ample evidence that the fencing simply pushed migrants to more vulnerable sections of the border. The total number of apprehensions along the southwest border in fiscal year 2004 was about 1.2 million, nearly identical to the figure in fiscal year 1992.

During that time, the U.S. Border Patrol’s busiest stations switched from San Diego to Tucson and Yuma in Arizona. Another consequence of shutting down border crossings in urban areas is that illegal immigration across the desert became more dangerous. Migrant deaths shot up from an average of 200 a year in the early 1990s to 472 in 2005.

Experts: Border Control Must Be Comprehensive
To experts, the lesson is clear: Immigration enforcement has to be comprehensive. Physical barriers are of limited utility without enough agents to police the border and detention space to hold those apprehended. Trump’s plan also accounts for those things.

[lz_table title=”Border Barrier: Before & After” source=”Congressional Research Service”]Border apprehensions in San Diego Sector before and after fencing.
|Station,FY 1992,FY 2004
Imperial Beach,202 173,9 112
Chula Vista,158 952,9 923
Other areas,204 456,119 293
[/lz_table]

“What works in Brownsville isn’t necessarily going to work in San Diego,” said Chris Cabrera, vice president of the National Border Patrol Council. “Whatever we have, you’re going to need technology to with it, as well … It can’t stand alone. You need to back it up. You need manpower.”

Cabrera said physical barriers tend to work best in urban areas. That is why the San Diego fencing was so effective, he added.

“It was more of a funnel system,” he said. “We wanted to push people from more populated areas to more rural areas where it’s easier to apprehend them.”

Over the rest of the nearly 2,000-mile border, the United States has a variety of barriers. Some sections have permanent vehicle barriers — steel posts or bollards driven five feet into the ground and encased on concrete. They are designed to stop migrants from driving across the border in rural areas.

Other spots have temporary barriers — welded metal, like railroad track, telephone polls, or piping that can be moved by forklift.

In an interview with Sean Hannity on Fox News Channel last week, Trump derided the “little toy walls” that currently exist. Judd, president of the border patrol union, agreed upgrades are need, although he added that he does not know which barriers can be improved and which ones should simply be bulldozed and replaced completely.

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Cabrera said the most effective strategy in some spots is “virtual offenses” that rely on sensors to track border crossers.

“There’s particularly going to be a focus on replacing fencing that is absolutely in atrocious condition,” Judd said.

Trump has indicated a desire to move fast, beginning construction in a matter of months. Judd and Cabrera agreed that is a doable goal.

“Government is only as slow as we let it,” Cabrera said. “He [is] from a business background, which is different from a government background.”