Graham wrote: I have tried many different tools over the years.
My favorite is the inflatable ball! This leaves absolutely no marks on the watch, and even opens some of my Rolex watches! Seeing is believing. Just make sure you buy the good quality version. The cheap ones don't work as well. http://www.ofrei.com/page1226.html
I agree, these work great, have yet to find a back I couldn't remove with it