No water bags for me! I like Arnes method, though I would always use a self choking line as a back up around the mast then attached to me/seat. the system i use is the same as i use in work (tree surgeon) one end of the halyard fixed to the harness the other attached to the harness via a friction hitch (prusik), then my backup which just moves up with me (redundant until loaded by halyard failure). i also carry a sling so once up i can choke the sling off and stand in the loop! should the worst happen and the halyard fail, coming down is simply done by alternating the loads on both backup and sling, moving them down in stages. sounds more complicated than it is, maybe i will take some pics and post them.
si