Regarding securing wood posts in concrete, I spoke with a fellow who made the following recommendation:

Wrap the bottom of the with an adhesive water/ice barrier. A brand name that I found is made by a comapny called "Grace." This stuff is like a roll of very thick tar paper, or a shingle without the rough particles on the outside. Through the water barrier, place re-bar into the post that will secure the post in the concrete. Set the post in the hole, and pour in the concrete, enough so it doesn't go over the water barrier.

This is the simplest way to secure a post without having the concrete touch the wood. -- Tim