On Tue, 16 Oct 2012 16:06:56 -0700 (PDT), gary
wrote:

4 x 4 redwood posts are bolted to the straps in concrete piers.

When replacing the posts, how can I prevent the bottom of the posts from deteriorating/rotting?

They do make a metal post holder that keeps them off the ground. You
put an anchor into the concrete, bolt the holder in place, then nail
or screw the post through the flanges.

In any case, I'd put some Penofin oil on the post ends anyway. Should
last decades like that.

http://www.homedepot.com/buy/simpson...se-abu44z.html

http://www.strongtie.com/products/co...BA-ABE-ABU.asp