Some have successfully used fence post anchors.
Replace rotted fence post in concrete.
Make the hole large.
How to replace fence post anchors in concrete or fence post spikes without concrete.
You can apply the solution by brushing it onto the post or dipping the post into a tub filled with the liquid.
The idea it to make a little ramp so water flows away from the wooden post on all 4 sides.
Using a small shovel to slope the concrete away from the post.
This way the post will not be sitting in cement to rot off again.
After putting the 3 bags worth of concrete into the hole and ensuring it nicely surrounded the post i used a small garden shovel to slope the concrete away from the fence post.
If you have an old wood fence post that is completely rotted off and you are able to remove it along with all debris you could reuse the cement ball for a new post.
Make sure your hole is.
Mark cut lines onto post with a layout square.
Look for copper naphthenate solutions at home improvement and paint stores.
Use a sledgehammer to break up the concrete around the old post.
Remove the old post.
Dig a semicircular hole around one side of the concrete pier.
Set the depth of cut on a circular saw to cut through the posts but not into the rails.
Knock out the wood between the cuts with a hammer.
Break up the concrete.