So I have a few people trolling on my site. I have this code in php:

$userip = $_SERVER['REMOTE_ADDR'];

I try to use this to ban that particular ip. But the problem is that some of these users have some sort of an ip changer software on their machines so they just come back under a new ip. Is this something the collective hacker mind can help me with? Is there a better way of determining users ip address in PHP?