In misc.rural David L wrote:
All my fence posts are set in concrete which has been domed up from
the earth allowing the water/soil to drain away from the base.

I can't think of the exact material, but isn't there some kind of
cheap tough plastic to nail around the base of the post? Gallon size
commercial gardening container? Maybe a shot of grass killer at the
base?

I've been pretty happy with using corregated draintile, about a 1'
length or so. Looks kinda goofy, but keeps my weedwhacker from
cutting 'em down