SAN FRANCISCO — Public urination has gotten so bad in San Francisco that the city has painted nine walls with a repellent paint that makes pee spray back on the offender.

It’s the latest effort to address a chronic problem in a city where the public works director calls himself Mr. Clean: Walls are coated with a clear, liquid-repellent material that goes on much like paint. Hit with urine, it splashes back on a person’s shoes and pants.

Mohammed Nuru, director of San Francisco’s public works department, says offenders will need to make the mistake only once to get the idea.

“If you have to go,” he said, “go in the right place.”

Nuru got the idea from Germany, where walls in Hamburg’s St. Pauli quarter are painted with the material to encourage late-night beer drinkers to find a bathroom rather than an alleyway.

A San Francisco light pole corroded by urine recently fell on a car. The city appears to be the only one in the nation using the paint, and it’s already receiving a stream of queries.

“We are getting calls from all over the place: Washington, D.C., Hawaii and Oakland,” said Nuru.

Signs hanging above some walls read: “Hold it! This wall is not a public restroom. Please respect San Francisco and seek relief in an appropriate place.”

Other efforts also are underway.

Solar-powered toilets roll through city streets several afternoons a week, attendants are manning public toilets to encourage people to use them, and city crews will check thousands of light posts to make sure they won’t topple.

Public urination is illegal, but a fine of up to $500 passed in 2002 has seen little success.