How save ip of user, who use random generated ip?

[ToeTagger]

in my project i need to allow rating system for users only once.i have a table in my database, where i store all ip addresses, and i check, if the user's ip is not in database, i allow rating.But now i met a problem.There are providers, that generate random ip addresses every time user restart computer.So when i call \[code\]$ip=$_SERVER['REMOTE_ADDR'];\[/code\], every time it returns different result from the same computer.I also tried something like \[code\]if (!empty($_SERVER['HTTP_CLIENT_IP'])) //check ip from share internet { $ip=$_SERVER['HTTP_CLIENT_IP']; } elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) //to check ip is pass from proxy { $ip=$_SERVER['HTTP_X_FORWARDED_FOR']; } else { $ip=$_SERVER['REMOTE_ADDR']; }\[/code\]But it doesn't help.How can i solve this problem?Thanks much