Florida Fence Posts

Building a 6' tall horizontal fence with 4x4 PT posts and a combination of horizontal 1x6 and 1x4 PT members (with 3/4" gap between boards). Florida building code calls for 4' spacing of posts and 24" depth with concrete footers. I would like to skip the concrete and use pea gravel to avoid future rotting. I also don't want the extra expense of transporting and pouring concrete (even if I pour it dry and let groundwater cure it). I already placed the order for 8' fence posts (buried 24" in gravel), but am wondering if I should buy 10' posts and bury 4' in gravel. I have an auger with extensions, so hole depth isn't an issue. Soil is very sandy in Florida and area where posts go is elevated, but bordering a rainwater drainage ditch. The ditch only fills after very heavy rains and will drain from sandy soil in about 1 day.

My 2 questions are:

For a 6' fence, 10' 4x4 or 8' 4x4? Pea gravel packed.
For 4x4 posts, should I use a 6" auger bit or 4" auger bit?

Thanks

I'm in the N.E. U.S. and I've never found a benefit nor especially a use for concrete in fencing and the few fences I've done over the decades are all still standing just how I left them. In your case, I'd agree that you need something to shoulder against the sand and Tamped gravel works great.

- So yes, go to the 4' depth, any 6' fence should have its posts sunk a minimum of 3'. And yes, go with the 6" auger for a bigger gravel pit, you want as big a pocket as possible so it can't push through to the sand. Even stainless steel screw-on a bigger square of composite, PT wood or heavy aluminum (diamond plate works well) to the post bottom to vastly improve lift resistance.

- Keep the fence pickets or panels 1/2" away from the ground, to avoid rot. For enjoyable lawn mowing with no need for weeding nor edging, put a composite (or PT) 1x6 under the pickets or panels and notch them around the posts.