Place I bought  almost 50 yrs ago,   had the typical  3 wire  barb fence around it.. and  mostly  wood posts  harvested  right off the place.  The owner said he, as a kid,  would help his dad  cut green,  post size limbs  off the  scrub oaks..  then  lash them to a cable and  float the whole raft out into the pond.     

after a year or 2,  they'd reel them in, cut to length, split if too large,   and stacked to dry.

These things were ancient when I bought the place.. and  next to impossible to  drive a staple into.   While they do degrade,  it's  from the outside-in.   They just get smaller and smaller in diameter as time marches on.  But the interior remains  like iron.   Most of the time  using a t-post type connection is the only way to attach the barbed wire to the post.    Which is good,  as a  rusted-in staple will break the wire  under snow- 
Pulling one out of the ground-  the part that was in the ground is almost  the  original  diameter,  but  getting cheesy.     
Not bad for  almost 100 YO  untreated posts,    compared to a current   $20 line post that  might make it  10 years.    


I wonder if any  variety of  wood  would  respond to water curing (I guess it would be an anaerobic process)  in this fashion that would give similar results?