Much of it will depend on your fence design. Are you designing a sail, or will wind pass through it readily? What diameter and height posts are you using?
40 years ago all we did was pound stones in around the post to hold them, that worked for 100s of years so yes either could be used, after 13 years you post was rotten at ground level and the trick is to protect the post from moisture and air and insects at ground level
Postsaver 5 in. x 5 in. or 6 in. Dia Rot Protection Sleeve (10 Pack) | The Home Depot Canada
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3 feet in the ground is good.
Yes concrete a little higher will help.Can the postmaster be melted on with something other than a blow torch?
also, Does topping the concrete above ground level and sloping the concrete away help? My concrete was below ground level so I imagine that allowed the soil , water, etc to eat at it.
Yes Yes Yes ! People, STOP using wooden fence posts - use Schedule 80 pipe set in a min. 10" dia. 3' deep hole filled with concrete for posts !Personally, I would never use a wood fence post. Always used metal (even 60 years ago) and those fences are still standing.
Yes, but those logs were completely submerged. They were not 80% sticking out above the water. So those old submerged logs are not like wood fence posts. Besides those old logs are better quality than the junk that is now sold as wood fence posts.Trapped water without air is not a problem. They harvest logs that have been in lakes for a 100 years