Jim Zimmerlin thank you very much! Good advise!

I purchased it onboard. I do that for almost all of the excursions we take on our cruises. I think it's better to do it that way, as there are risks that you take when you book independently... and some peace-of-mind advantages to booking through the cruise line. This outweighs any possible minimal savings one might have from booking independently. The only time I would consider booking a shore excursion independently would be to get some unique experience that the cruise ship does not offer.