Sen. Bill Frist (R-Tenn.), pushing for a fence, armed with a blog, pimps this stat:
Take the case of San Diego. According to the FBI Crime Index, crime in San Diego County dropped 56.3% between 1989 and 2000, after a fence stretching from the Ocean to the mountains near San Diego was substantially completed. And, according to numbers provided by the San Diego Sector Border Patrol in February 2004, apprehensions decreased from 531,689 in 1993 to 111,515 in 2003.
That's why I strongly support the Secure Fence Act of 2006.
Warren Meyer has a thorough debunking, starting with the cherry-picked time frame—during which crime dropped in large measure throughout the country. (Comments Meyer: "The border fence in San Diego even had a similarly large effect on crime in New York State! That thing is amazing.") Further, the stadium light-laden, two-layered, fancy-pants fence Frist is frothing after only went up in 1996, making the souped-up version an unlikely candidate for explaining a decade-long drop in crime.