SACRAMENTO, Calif. -- California parole officials said Friday they have ordered increased monitoring of all sex offenders after recent high-profile lapses, most notably in the case of a young woman who was held captive for 18 years by a convicted rapist.

The new policy requires parole agents to more closely track the movements of offenders using GPS-linked ankle bracelets.

It also requires agents to visit high-risk sex offenders at their homes twice a month, up from just one monthly visit.

The policy change memo independently obtained by The Associated Press came after agents were criticized for not discovering a convicted sex offender was allegedly keeping Jaycee Dugard hidden at his Contra Costa County home for 18 years.

Corrections officials are also reviewing whether they should have revoked the parole of John Albert Gardner III, a convicted sex offender now charged with murdering Poway teen Chelsea King and being investigated in the death of Escondido teen Amber Dubois.

"We basically have higher level tracking not only on high-risk sex offenders but even on low-risk sex offenders," said Gordon Hinkle, spokesman for the California Department of Corrections and Rehabilitation. "This is basically areas that we felt needed improvement."

The policy changes are a response to a report in November from the department's inspector general that criticized it for missing chances to catch Phillip Garrido, who is now charged with kidnapping and sexual assault in the Dugard case.

"Public safety is of paramount importance," Margarita Perez, deputy director of the department's Division of Adult Parole Operations, said in the policy memo distributed to parole agents on Thursday.

Authorities say the convicted rapist fathered two children with Dugard after she was taken from a South Lake Tahoe street in 1991, when she was 11.

Garrido and his wife, Nancy Garrido, have pleaded not guilty.

The new policy requires increased use of GPS tracking of those considered less likely to re-offend.

Forty lower-risk offenders are supervised by each parole agent, compared to 20 high-risk offenders per agent.

Melinda Silva, president of the Parole Agents Association of California, predicted the increased workload will overwhelm agents charged with tracking the movements of 40 sex offenders.

"We need to get them to 20-to-one," she said. "If they want to improve supervision, they've got to reduce caseload."

The change in policy also followed questions over the monitoring of Gardner, who has pleaded not guilty to murdering 17-year-old Chelsea King and assaulting another woman in the same park north of San Diego.

He also is under investigation but has not been charged in the slaying of 14-year-old Amber Dubois.

Records show officials decided not to send Gardner back to prison, even though he violated a condition of his parole by living too close to a daycare center.