Did you say it is rotten at the root end? I only see a bent

piece. If it is only bent, just bend it back. Every once in a while I have a deer bump itself against my pool fence in panic and get caught between two pieces... I have to bend them back.

If the root is rotten then it is another matter. You have to replace them. 

Watch this video how to mount rail post on brick:

the price is about 100 dollar per side, and probable  4 hours for both sides labor time.