What Fence posts are people using in wet ground?

The ones treated with copper oil should be reasonably good. Tanalized posts are based on a water based copper so will leach away the treatment and rot much quicker.

Copper naphtanate gives timber a very long life in USA and aus under tougher conditions. The question I can't find an answer to is how similar the EU approved copper oil treatments are to the copper naphtanate ones widely used elsewhere.

Yes lost in hedge. No can't lay it right enough. But it's been hedge cut every year since and is fairly thick. Any gaps can be filled with quicks to do away with laying. Put it this way, he hadn't bought posts in 25 years, and can't see any Nedd for them in the next 25.