In classic cake fashion I will now enter in the conversation without reading all the prior posts:
You can't ban anyone from a public server. Its a fundamentally flawed concept. Put simply, there are infinite IPs, locations, handles, etkeys nicks etc out there for someone to choose from and join the server. You cannot ban them all. The most you can do is 'keep up'. So for this reason you have two choices and only two choices:
[*]Continually ban his latest IP, handle, etkey and continue this forever, being a pain every time.
[*]Make OZ-ET server an invite-only system. Require approval on every person who joins. (server will die instantly)
In my opinion the only thing that we can do is make it more fun to behave than to misbehave. Half the fun of misbehaving is ban-evading. If you take the challenge away then there will be no fun.
* the whole cake has 10+ years experience of ban evading and trolling. He is considered an expert in online trolling, harassment and general cakeness.