Need fastener recommendations please

I must have driven a thousand of those square drive SS 18-8 screws into treated pine decks and they have not rotted. when I pull them to replace som rotten boards, they are perfect.

On my wood boat, all screws above the waterline where I used SS deck screws have been fine since I got the boat in 1998. Like screwing down teak deck boards, plywood floors, toerails, reconstructing flybridge and some in the upper hull.

But any SS screws below, sitting in brackish Chesapeake bay water and continuously wet wood, they crevice corrode terribly in a few years. they get channeled and pierced with holes.