Here's my method:
I have a static
line attached to the mast, top to bottom. To climb this
line, I use standard climbing
harness and ascenders w/ foot loops. The safety line is a halyard TIED OFF to strong points on the deck, which is attached to me via 2 lines with prussiks on the halyard. I also use a webbing strap that goes from one side of my
harness, around the mast, to the other side. This is to keep me within grabbing distance of the mast no matter how the boat moves.
NOTE: This is the system that works for ME. I designed it from climbing gear I aleady had, and the fact that I don't trust anyone else to haul me up. I find it comfortable enough to run up the mast at
anchor for pictures. And yes, it is slow, but who cares??