The National Center for Preservation Technology and Training (www.ncptt.nps.gov) has 158 articles, with pictures, on headstone repairs and cemeteries etc.
Association for Gravestone Studies has a list of over 100 ways people have said died on headstones.
A less invasive way to read headstone carvings is to reflect sunlight using a mirror. Harsh cleanser use can cause as much damage in one day as 50 years of erosion from the weather.