Thanks Diverchaz, scubalarry54, and eastcoastdiverLLC for your responses. I just got back from a week in the Mayan Riviera. Between 4 days of torrential downpours and thunderstorms, I managed to squeeze in a day of reef diving and 4 cavern tours. The cenotes were definitely the highlights of this trip. From what I’ve seen and heard, Bil Phillips at www.speleotech.com is THE place to get cave-certified. I can’t wait to go back and take a cave course!