You're right that the best place is your head.
However, IMO the method you describe will merely prevent the Script Kiddie style bots which try common passwords. Other than those all the method you give does is introduce another documented level of cryptographic hashing to what will mostly be a human decided pair by some system. Therefore any cracker who profiles you as an individual and knows the definitely not random habits of human choosing will still be able to crack this. If you look around the web you'll find many security experts advise for password security you need lots of _real_ entropy not human pseudo-random 'imagination' and definitely not anything based on a system or it's one cracked, all cracked.
