San Francisco is testing pee-resistant walls on city buildings to cut down on the side effects of people seeking relief. The move is relatively expensive so officials will wait to see how effective it is before extending the program.

According to SF Gate, the city has received 375 requests to clean up urine in the streets in the past six months, around five percent of all cleaning.

The city already runs a program called Pit Stop, which involves putting up temporary toilets overnight in areas where public urination is a particular problem, funded by advertising. That’s only partially reduced the extent of the problem, while a program of fines for public urination seem to have little effect, possibly because it relies on people being caught in the act.

Instead officials are trying out a commercial hydrophobic coating named Ultra-Ever Dry, which is more commonly used to protect materials from contamination, corrosion and the formation of ice.

The coating has two layers, one which bonds to the wall. The other layer “is comprised of patterns of geometric shapes and billions of interstitial spaces.” The effect is a series of tiny peaks, with part of each water droplet touching only this peak and the rest of the droplet not touching the coating or the wall at all.

In this particular set-up, the idea is not only that the urine won’t touch the wall, but it will be bounced back directly onto the person who produced it, acting as a deterrent. Early testing suggests the liquid is bounced back with more power than originally anticipated.

So far nine walls have been painted at a cost of “several hundred dollars” per wall. Officials say they will check whether it has worked via visual inspection. It remains to be seen whether those caught short will be prepared to experiment with approaching the wall at an angle.

The tactic is based on a similar approach used in Hamburg, Germany, where public urinators go by the wonderful name of “wildpinklers.”