The problem begins with the shape the holes normally take.
Fence post footing detail.
The starter bars should protrude out of the concrete at spacings roughly 1m or equal to the holes in the blocks.
Recommended wood fence post foundation details h height of fence above grade feet s spacing of fence posts center to center feet b diameter of round concrete pier hole or dimension of square pier inches d required depth of concrete pier feet and inches p post size wood nominal inches foundation post type and size b 12.
The depth of your fence post footings will vary according to fence height wind loading and soil type as well as other factors.
Recommended steel fence post foundation details h height of fence above grade feet s spacing of fence posts center to center feet b diameter of round concrete pier hole or dimension of square pier inches d required depth of concrete pier feet and inches p post size galvanized steel schedule 40 outside diameter od inches center to galvanized steel post.
Caulk around the fence post base apply high quality exterior acrylic latex caulk or silicone specifically designed to adhere to concrete at the base of the post.
The footing should contain reinforcement steel and starter bars.
The standard rule of thumb is to bury at least a third of the length of the fence post in the ground half is better but local building codes may require a minimum depth such as 30 inches so.
But surprisingly even digging holes and filling them with concrete is fraught with difficulties.
Setting fence posts so that they re plumb and evenly spaced is part of the challenge.
Do apply caulk to each fence post after only an hour cts rapid set concrete mix will have hardened completely.
You might consider the job done but to further safeguard the fence post against rot.