To use:

$ xlock password

Whenever you hit enter, the program will look for password in it's
recent input.

The majority of the coding is from Ian Jackson's xtrlock (X
Transparent Lock), I picked what I wanted to use from that script and
changed it to use an inputted string for the password instead of the
user's password.

I hacked this together very quickly so I have no idea what sort of
bugs it might have. I haven't actually read through all of the
coding. It does not appear to interrupt calls such as C-M-Backspace
and C-M-Fn so you have a simple way out if it breaks.

Use at your own risk!