Ratty, each job I do regards Wood Posts ( a few, but not that many) before entering the post into the ground I put grease on the post then wrap it with a plastic Bag, then use concrete to secure, you can cut off the Soiled / rotton base & reuse the post, I done that last week on a job I'd done, I dug out the rotten post base out of the concrete, cut it square about a Foot, built up the Original area within the concrete where the post had been, wrapped the bag in grease then refilled. job done.