On the Tropic of Cancer, read interesting latitude info and why straight sticks produce no shadow only one or two times a year. And why 1000 years ago it was different. Cache is above a very large cleat the ferry used to use. Disguised in shells the locals will avoid.
Go fishing on the bridge with the treasure. Goat island to the west was the home of the ferry operators. Could have real pirate treasure caches. Sorry, not giving coordinates to them.
Small note on cache maintenance: I own a house 2 miles from the site and visit 3 times a year. I have 9 partners in the house, who will also check the site.