function clean_url($string) {
// Make lower case.
$string = strtolower( $string) ;
// Make alphanumeric. Remove all characters.
$string = preg_replace("/[^a-z0-9_\s-]/", "", $string);
// Clean multiple dashes and whitespace.
$string = preg_replace("/[\s-]+/", " ", $string);
//Convert whitespaces and underscore to dash.
$string = preg_replace("/[\s_]/", "-", $string);
return $string;
}