RotUrl: encode/obfuscate URLs for use in other URLs

rotUrl.php

<?php

/**
 * Rot35 for URLs. To avoid increasing size during urlencode(), commonly encoded
 * chars are mapped to more rarely used chars (end of the uppercase alpha).
 *
 * @param string $url
 * @return string
 */
function rotUrl($url) {
    return strtr($url,
        './-:?=&%# ZQXJKVWPY abcdefghijklmnopqrstuvwxyz123456789ABCDEFGHILMNORSTU',
        'ZQXJKVWPY ./-:?=&%# 123456789ABCDEFGHILMNORSTUabcdefghijklmnopqrstuvwxyz');
}

We must save this conversation here as a future usage note tho.
So for safe usage

urlencode(rotUrl($url)) // to encode 
rotUrl(urldecode($url)) // to decode 

http://codepad.org/rz0faInK