Tim Downie wrote:
I'm in the process of taking down a hedge and putting up a new fence and
I've found that in some areas, the ground is waterlogged to within a couple
of inches of the surface.

The plan was for a ranch style fence with 4"x4" tanalised posts at 6'
intervals and I'm wondering what's the best way to set the posts to give
them the greatest longevity.

Concrete posts?
Steel 'metpost' type holders?