SAN FRANCISCO — Public urination has gotten so bad in San Francisco the city has painted nine walls with a repellant 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 repellant 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 alley.

Public urination has long been a problem in San Francisco, where a light pole corroded by urine recently fell on a car. The city appears to be the only one in the nation using Ultra-Ever Dry from a Florida-based company, and it’s already receiving a stream of queries about the product’s success.

“We are getting calls from all over the place: Washington, D.C., Hawaii and Oakland,” said Nuru, who Tweets under the handle (at)MrCleanSF.