Thanks for the comments folks. Just having a rant.
The Northumberland & Durham recording project are under strict instructions not to clean stones and will photograph what they see (or don't see) at a site which I think is sensible. A major part of the record will be an assessment of environmental threats at each panel - vegetation growth, cattle, sheep etc. I suspect we still know very little about the factors affecting how the rock erodes but I hate to see stones harshly scrubbed. I think the evidence we see out in the field is that the motifs fare better when they have been covered up. We all need to take extra care of them when their positions become more widely known. Then they'll last for a few more years.

Liked the Matfen stone photo, Hob - very atmospheric. Good posts all round on this site. Certainly looks fun for rock art hunters in Scotland (and Ireland). Great discoveries.

The Rock Art Meeting sounds interesting, Stonenicker. It'll be good to meet some of you other fanatics. Must look in my diary ....