“Graffiti is not going away ever,” says Thomas Corrales, 53, who works for the Los Angeles Department of Public Works training and overseeing crews of graffiti cleaners. Some 175 cleaners fan out across the city every day; in the second half of last year, they removed 3.5 million square feet of graffiti. Corrales grew up in a neighborhood where spray-painted tags were so pervasive that he became almost blind to them. Then one day in 1993, the unemployment office got him a graffiti-abatement job. Now he can’t help spotting even the tiniest Sharpie tags.

Unauthorized paint on a wall can be many things — art, hate speech, social and political messaging, vandalism, the claiming of space. However it manifests, it often has a multiplier effect: Graffiti begets more graffiti, and tags will be tagged over. On occasion, when Corrales paints over graffiti, someone shows up to tag it anew before he can even drive away. Remember that humans have been marking up walls for millenniums; don’t get angry or take it personally. “We’re trained not to confront anyone,” Corrales says. If you ever feel unsafe, leave and come back later. Wear long pants and boots, preferably the steel-toed kind if you plan to use a water blaster (water sprayed at 3,500 pounds per square inch can take off skin).

As you traverse streets, carry the paint colors you’re most likely to need, including gray, beige, tan and white. If you don’t have the exact color, use a spectrophotometer to measure hue and make a match. For walls, paint with either a roller or a paint sprayer. For stop signs, murals and most metal surfaces, use a water-based chemical remover mostly known by its brand name, Krud Kutter. City-approved murals are sealed with a clear coat that makes them easier to wipe clean. For the multistory spatterings that people make by filling fire hoses with paint and shooting it out with a fire extinguisher, you’ll want cherry-picker trucks. Clean sidewalks with a high-pressure water and sand blaster.

Cityscapes are covered in layer after layer of paint, like an ever thickening skin. Never get attached to a clean, monochromatic surface. “You know that it’s going to be retagged,” Corrales says. “And you’re going to come back again, too.”