Some have successfully used fence post anchors.
Replace rotted fence post in concrete.
Mark cut lines onto post with a layout square.
Knock out the wood between the cuts with a hammer.
Make the hole large.
You can apply the solution by brushing it onto the post or dipping the post into a tub filled with the liquid.
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.
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.
Position the lines above and below each horizontal rail.
Project step by step 5 dig the right size hole.
Set the depth of cut on a circular saw to cut through the posts but not into the rails.
Look for copper naphthenate solutions at home improvement and paint stores.
Remove the old post.
Dig a semicircular hole around one side of the concrete pier.
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.
Break up the concrete.
Saw along each pencil line.