make password invalid once logged out of password protected page

In a wp-based site I have a custom form which I needed to hide from general public and give access to only a selected few who would then get a password from me, enter it and access the form and submit it. On form-submit I redirect them to another page. I have employed this bit of code below in my functions.php, which logs them out of the password-protected page, once redirected.

add_action( 'wp', 'post_pw_sess_expire' );
    function post_pw_sess_expire() {
    if ( isset( $_COOKIE['wp-postpass_' . COOKIEHASH] ) )
    // Setting a time of 0 in setcookie() forces the cookie to expire with the session
    setcookie('wp-postpass_' . COOKIEHASH, '', 0, COOKIEPATH);
}

Now the twist, once any of these selected few are logged out of the password-protected page, I needed the password to become invalid. Not necessarily but sort of like a one-time password. Let me know if it is possible or either ways. A solution would be great if not please give me some pointers or alternatives. Thanks in advance.