It's not suitable for all applications, but you can send failed logins to some innocuous page. Apache's ErrorDocument setting in .htaccess can be used for that. You can point that to a perl script which logs whatever you want to see and produces a joke, a stunt, or just something harmless which must be parsed to discover that a guess has failed.

That way you don't need a doomed effort to maintain state, as merlyn explained, in a stateless protocol. All you've done is make guesses more time-consuming and difficult. That's how passwords are supposed to work.

After Compline,
Zaxo