On Wednesday, May 13, 2015 at 10:31:44 AM UTC+1, Tim Lamb wrote:
In message , Ian Jackson
writes
In message , Jacko
writes

Sure, but it is unlikely to stop the wood rotting
where it is in contact with wet soil or concrete.

If you fill up the hole, and leave it for an hour or so, you will
probably find that the preservative has vanished. Where has it gone?
Has it evaporated? No - it has soaked into the wood. So you top it up a
few times more, until it the wood has absorbed as much as it can. If
you repeat the treatment once in a while - especially when the post is
getting a bit old and the original preservative is becoming less
effective, I think you'll find that it will forestall the evil day when
the rot eventually begins to set in.

I think this would work if you have the patience:-) Telephone poles are
routinely dug around and then treated with some chemical preservative.

Look up Boron as a timber preservative.

Some years ago, I noticed what appeared to be large nails hammered into
timber electricity poles at ground level. The guy I asked said he
thought they were to extend the life of the pole.

--
Tim Lamb

Round here telegraph poles are pressure treated.

About 20 years ago we put a fence around a vegetable garden to keep out the wabbits.

After shooting and eating same wabbits they ceased to be a problem so last year I had occasion to remove the fence. The only posts that hadn't rotted were the few we had used to finish off the job which were standard round fence posts as supplied by the forestry people. All the other posts were pressure treated and survived very well.

IME forget concrete. Dig a hole. Few stones in the bottom and back fill with soil well tamped down and more stones if you have them. Most fences are quite solid in a side to side manner as they gain support from their neighbours. Its the to and fro that causes the problems