Karl I will also put in a vote for using resistance training, if you can get into it.

Especially from a diving perspective -- using free weights (instead of machines) is supposed to help with strengthening 'stabilizer muscles' instead of just one specific muscle group, allowing you to help stabilize things better while climbing up the ladder on a rocking boat, and other such benefits.

Somewhere around here I have a copy of Fitness for Divers. Might also be something to consider.
http://www.divefitness.com/html/guides.h....