Steve Chapman

Some of the fence is supposed to traverse creek beds that occasionally play host to violent flash floods. "You are going to have to build hundreds of culverts big enough for debris the size of brush and small trees to float through the length of the border," said another former federal agent. "If it is wide enough for bushes to get through, then people can get through."

And what will this lengthy barrier accomplish if and when it is finished? It will certainly prevent transient Mexicans and Central Americans from crossing the border in the places where it stands. But it won't prevent them from crossing elsewhere, as they did when fences were erected in the San Diego and El Paso areas. Since the government began cracking down in those places, total illegal immigration has actually risen.

Instead of making their way through urban areas, undocumented foreigners have eluded capture by trekking across remote deserts and mountains, paying human smugglers to shepherd them into the United States. Instead of snaring more illegal entrants, we're now arresting fewer.

Research by Princeton University sociologist Douglas Massey indicates that the chance of being nabbed has dropped from about 33 percent 25 years ago to about 5 percent today -- while the cost to the Border Patrol per apprehension has soared. At the same time, the fatality rate of those crossing has tripled. Not exactly a proud achievement: killing trespassers instead of catching them.

A longer, more formidable fence can once again divert illegal immigrants to more dangerous routes and increase the fees charged by smugglers to arrange passage. As long as higher-paying employment beckons to impoverished people on the other side of the border, though, the cost and risk will still look modest next to the potential payoff. The fence can make illegal entry harder, but it won't make it any less popular.

Steve Chapman

Steve Chapman is a columnist and editorial writer for the Chicago Tribune.

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