Arizona's recent passage of a law vastly expanding the power of local law enforcement agencies to detect and detain possible undocumented migrants has helped spark national debate on immigration policy. Currently, the centerpiece of that policy—in which nearly every party on every side says fails to address the fundamental economic and social issues that lead to migration in the first place—involves the building of border barriers that attempt to physically prevent frontier crossings. About a dozen variations of the "Border Fence" are currently in use; here's a list—and a quick evaluation—of six of the most popular types.

Type: Landing Mat

Technology: What technology?

Status: Obsolete, in need of replacement

The Landing Mat is the oldest border fence still in use. Construction is corrugated steel, usually about 10 feet high, and the raw materials and name come from the former life of the fence panels—they were used as portable touchdown pads for helicopters operating in Vietnam. The Landing Mat can be easy to foil, since Border Patrol agents can't see what's going on on the other side. Cutting a hole in the Landing Mat with a power saw is a relatively easy job, and the inefficiency of the style means that the Landing Mat is high on the list for replacement by high-tech types, though it remains in use in every border state except Texas.

Type: SBInet

Technology: Electronic

Status: Under construction, but future uncertain

SBINet stands for "Strategic Borders Initiative—Networked." This is the much promised, and so far undelivered, "virtual" fence. Built by Boeing and employing buried sensors and camera towers all linked to central control centers, SBINet is designed to detect and track border crossers and automatically dispatch field agents to intercept. The problem? At least $1.1 billion has already been spent on different iterations of the virtual fence, and none has worked. False positives, slow radio response and problems with wind led Homeland Security secretary Janet Napolitano to question the worth of the entire project last January. Despite this, the latest generation of tower—with a promised increase in effectiveness—is now being tested south of Tucson.

Type: DIY

Technology: Crowdsourcing

Status: Controversial, sometimes nutty, but gaining official acceptance

Frustrated residents of border states, as well as pressure groups, including the so-called Minutemen, say that official fence types are inefficient and too expensive. That has led to a series of projects ranging from conventional barriers on private, border-adjacent property to high-tech monitoring systems (some of which use hobbyist remote-control aircraft for monitoring.) The type recently got a level of official blessing when Texas governor Rick Perry joined with local law enforcement agencies to construct a network of cameras, designed to be monitored by the public via the Internet.

Type: Aesthetic

Technology:Technology: Not applicable, though it may combine elements of other fence styles

Status: Still in use in sensitive border areas—usually in cities—where a barrier's symbolism is important

Though not entirely for looks, aesthetic fencing is designed primarily to soften the symbolic and visual impact of a barrier on both sides of the border. Examples of this include a fence with windows in Nogales, Mexico, and a proposed art-decorated wall that would adjoin the University of Brownsville in Texas.

Type: Bollard

Technology: Mostly brawn, but environmentally sensitive

Status: Being used less and less, though still active in key areas

Bollards are the fence style the average person is most likely to encounter, though in a different guise: They're the stubby, concrete-filled barriers that protect office buildings and shopping malls across the U.S. The bollard's sole purpose is to prevent vehicles from crashing through. Wildlife, whose habitat often spans both sides of the border, can easily pass. So can people.

Type: Normandy

Technology: As the name implies, World War II, with a little extra oomph

Status: Still common, especially in Arizona

Normandy fences are crisscrossed posts, lined with barbed wire or mesh, that were used during both World Wars to protect soldiers in foxholes. Modern Normandy designs use heavier steel and bollard-like filled posts. Designed to discourage both humans and vehicles, though fairly easy to circumvent by building an up-and-over wooden ramp.

Type: Anti-Ram

Technology: Refined conventional

Status: Rapidly becoming the most employed form of standard fencing—at an estimated cost of $3.8 million per mile

This fence type is the latest nonelectronic barrier used by the Border Patrol, and it is gradually replacing less sophisticated types. The fences are higher than the Landing Mat—which can be circumvented by pulling a van up alongside and having people jump from the roof—and are buried 6 feet deep to prevent tunneling. The fence is tested to withstand a 10,000-pound vehicle traveling at 40 mph and claimed to be virtually impervious to cutting.

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