I don't know about its distribution in Florida, but both Osage Orange (sometimes referred to as "hedge apple"
and white oak are very rot resistant. Further, if you have access to iron wood, locust, or thorn tree wood, those would be quite rot resistant as well.
Your best bet for interesting pieces is to find a swamp or river/streambed where a tree has either been uprooted or the erosion has caused the tree to fall, leaving the roots exposed. About 10 minutes with a chainsaw and a measuring tape should get you what you need. Then, use a high pressure power washer with just water to strip off the junk off the outside, and stick it in the freezer for a week (I left mine outside for 2 weeks in weather that was -30 F, but your chances of getting that in Florida are about as good as the Hoosiers going to the Rose Bowl next year).
Good luck,
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Homer W. Faucett III, esq.
Purveyor of Trivialities and Fine Nonsense