There are two headstones in Devon which I went to see a couple of years ago.  One of the stones in question had a beautiful rose bush right in front of it, and the stone itself was covered in lichen.  In spite of all the obstacles time and nature presented, I was able to obtain the details without adopting any harsh methods, which of course I wouldn't even think about doing.  Although I do confess to having used water in the past. 
The other stone - in the same churchyard in Bere Ferrers and opposite the main one - was completely illegible.  However when the sun moved position what was invisible became wonderfully clear.
Jayson