Even the ancient and natural Petroglyphs are vulnerable to graffiti. When vandals strike, they create a huge problem for the people who have to clean it up.

"All of the petroglyph areas are ecologically-sensitive, so when we look at trying to do any kind of graffiti repair, we have to be very cautious," said Albuquerque Open Spaces Director Matt Schmader.

The law only permits low-impact cleaning. Harsh chemicals and sand blasting are prohibited methods.

The City of Albuquerque discovered a product named "Elephant Snot."

"It is a biodegradable, environmentally-safe product," said Schmader.

Fortunately, the Parks and Recreation Department only needed to buy one gallon of Elephant Snot.