You know i actually didnt realise that you were discovering previously unrecorded rock-art. i though you were just taking photos of stuff that was out of the way.
Sounds like a lot of hard work, jeez the odds of just going out into a field and finding rock-art on random stones has to be massive, my mind is literally boggling at the moment. I know you are looking at areas where there is recorded art.
This is a link to an interesting find and shows it is possible to find new art.
http://www.mythicalireland.com/ancientsites/news/teltown-rock-art.htm