Well I’ve been replacing fence posts this weekend after Doris
Two post rotten and snapped. One was a 4″ post that has been in since before we had the house (>10 years). It was cemented in place but had rotted just above the cement line. That’s what happens
The other was a 3″ post I replaced about 5 years ago – same thing. So a 3″ post lasts about 5 years
Most durable fence will be with concrete posts – obviously won’t rot
4″ posts considerably better than 3″
A Picket fence is much less affected by wind – you could do a ‘double picket’ – slats both sides which will still allow the wind through but gives privacy
Or best of all a beech hedge