Jessica's Law, which took effect in October, is hard to argue with. Named after a little girl in Florida who was raped and killed, it prevents any sex offender on parole from living within 2,000 feet of a school or park. Even in liberal California, the proposition was passed by an astonishing 70 percent. But perhaps voters here would not have been so enthusiastic had they known about its unintended consequences.

In other parts of the state, paroled sex offenders have numerous housing options. But because San Francisco is so dense, there are virtually no neighborhoods that don't have a park or school. On a police map, Mission Bay shows up as OK for parolees, except most of the area's housing is still under construction. Other slivers that meet the 2,000-feet rule contain primarily office and retail spaces.

About 60 paroled sex offenders have been told to find a new place to live or be arrested. But where can they go? They can leave town, but another county has to agree to accept them, which requires a stringent screening process. The fear is that their only choice is to go underground, which would defeat the very purpose of the law. Indeed, 28 paroled sex offenders have already registered with police as "transient," which is another word for homeless (meaning they're more likely to hang out in -- you guessed it -- parks). In Iowa, which has a similar law that police are trying to get repealed, the number of sex offenders gone missing has reportedly skyrocketed.

According to police spokesman Sergeant Steve Mannina, homeless convicted molesters are more difficult to track because they're listed only by name in the online sex offender registry, not by geographic location. (Some people now consult that registry before buying a house.) Jessica's Law requires parolees to wear a GPS tracking unit, but good luck getting them to recharge it every night, especially if they're living on the street.

Jake Goldenflame, a convicted sex offender in San Francisco who runs a website and programs for those in recovery, says he hears from people who feel they have nothing to lose by going AWOL. (Goldenflame isn't subject to Jessica's Law because he served his prison and parole sentence years ago.) And he fears the end result. "Sex offenders are addicts," he says. "When they become depressed, they're going to self-medicate, and their medicine happens to be sex with kids. You pile too many stressors on a guy, and he's going to go off."

San Francisco leaders could plead their case before the legislature, but that's going to take time. Besides, when Assemblyman Mark Leno tried to warn lawmakers about the draconian consequences of the law, he was branded as being pro-child molester and soft on crime. At the very least, parents should know not to be lulled into a false sense of security about a well-meaning law.