How? I've been told (I'm not knowledgeable about this stuff) that it's pretty near impossible.
I'm guessing that the way the mods would choose to do this is by banning a particular IP address. Yes, that will allow these reporobates to continue to post via proxy. However, once they are detected, they are re-banned and all of their posts are removed. This is a process, not an event. But, think about it, if you had to go through all of the trouble to create a new username and post by proxy and each time you were detected all of your posts were removed, how long would you keep at it before you decided not to waste your time anymore?
This could be easily done for the few persistent trolls we now have here and it should be done straight away. Simply banning one troll
who posts here continuously would rid the forum of some 50 or more aliases. Let's enforce the current rules properly, re-evaluate and then decide if we actually need more rules. My bet is that if current policy is doggedly enforced, the trolling problem will be diminished.