advice on banning (PHP and javascript)

I currently own a chat site [[login to view URL]][1] and i am looking for some advice on how to ban members other than ip bans and cookie bans and if there is any other way to ban them from entering my chat site,my chat site is wrote in PHP and Javascript and can currently do IP bans but if a member gets banned they can easily change there ip and come back on,so i was wondering if there is any other way it can be done that can not easily be cracked like banning MAC or there HD serial