Seperating by '-' is not recommended, I think. If you'll explode these later, you'll surely will get errors. Some URL contains '-' to. Then you must use an "unique" seperate; like '|*@'36Y1' My way I would do it, is to throw each URL in a row.
Also, I would build up these database, existing out of an unique ID, IP, URL and timestamp.
Something like
$sql = "INSERT INTO `db` ( `id` , `ip` , `url` , `timestamp` ) VALUES ('', '".$_SERVER['REMOTE_ADDR']."', '".$_SERVER['PHP_SELF']."', '".time()."')';
mysql_query($sql);
Something like that, where id is an unique auto_increment.