Sinking telephone poles
Worked with lodgepole pine timbers for ages and we treated with a mixture of diesel and coppernapthanate. We soaked for quite awhile though and had tanks for such purposes. I am not sure you gain a lot trying to paint something on.
I don't think concrete will accelerate decay unless you somehow form a pocket the pole sits in and that traps water. We usually dry fit posts. We fit them in their holes, level and plumbed them, then poured in dry concrete mix and wet it down so it would set.
I think if you are burying these 8 feet repacking dirt would hold them.
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