Umm... close to the surface and in the wet zone in my experience. Treated posts in free draining soils last longer than those in *black* soils found on river flood plains.
Stored treated posts will crack as they dry further. My technique is to dip the post in whatever preservative comes to hand so that the point and at least 6" above finished soil level are immersed. Hopefully protecting the exposed interior.
Creosote is an effective preservative as there are stretches of treated Cedar post and rail fencing in favoured locations here which must have been installed prior to 1938.
I worked for a guy (sofftware architect) like that once. He was not only wrong, or even usually wrong (these are common in the trade), he was _always_ _utterly_ completely out of phase with the right answer.
Once you realised this, and once you became good enough at hiding what you were actualy doing, it all worked out surprisingly well.
Telegraph poles don't fail by rotting alone, they fail by breaking. Because they're so big and wind-loaded quite heavily, a "rotten" pole will snap long before it becomes "as rotten as a fencepost". Nor is this failure likely to happen just at ground level. So regular inspection is needed to ensure this is detected before it's a problem, and poles are (or ought to be) removed and destroyed before they're a hazard.
This ability to fail anywhere up the pole also means that soaking in along the end grain just isn't enough for them. They're too long for it to be effective, the risk is too great of rot around damage or attachment part way up for us just to rely on protecting their bases. So telegraph poles (even longer than railway sleepers) have long been subject to research and complicted treatments involving vacuum or pressure impregnation.
Soaking the bottom ends of vertical shed boards in creosote before assembly is a great way to protect them against rot at their likely rotting point. However it doesn't have much effect along the length of the board, nor is it effective as a treatment for big fenceposts (they rot at ground level, a big post's end is buried deeper than this).
Back it time to 2011, well its bloody hard to get nowadays and it used to smell wonderful in the sun. The new so called replacements are puny and seem to be of little use at all. Some people seem to make up concoctions using old engine oil and all sorts of stuff. Brian
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