What goes wrong with wood fences in Miami's climate?
Termites and rot
South Florida has both subterranean and drywood termites, and the ground stays damp for much of the year. Lumber that touches soil should be pressure treated and rated for ground contact. Even then, wood lives a shorter life here than in a dry state, so the grade of lumber and the care taken with the posts make a real difference.
Wind loads
Miami-Dade sits in the High Velocity Hurricane Zone under the Florida Building Code. A tight solid fence acts like a sail in a storm. Shadowbox and board on board styles let some air pass through, and deeper, well-set posts help the whole run hold. Ask what the fence is designed to handle, and do not expect any wood fence to be storm-proof.
Salt air and sun
Near the bay and the coast, salt speeds up rust on nails, screws and hinges. Hot-dip galvanized or stainless fasteners last longer than bright steel. Strong sun also dries and cracks bare boards, so plan on a sealer or stain.

