troll / spammer prevention

[CHNoodles]

We have a person spamming our message board. My first thought was to be to try to catch him at registration, and I saw a thread with one such hack:
https://vborg.vbsupport.ru/showthread.php?threadid=45092

But I'm wondering if there would be other ideas besides that to help us stop this person from returning. I could describe what the person does, but I'm not so sure it's a wise idea to do it publicly on the board. Can I post here what the person does, in the hopes that someone will have some suggestions for a hack to help us win the battle?

[Erwin]

Try the Hellban hack, or the Secretly ban a user hack.

[CHNoodles]

Thank you Erwin. I took a look at those, but they do not prevent a user from posting, only from others seeing his posts. I would like to prevent the user from even registering.
Do you think I should describe publicly in the forum what the person is doing? That might spark some ideas / suggestions.

[Logician]

I'm sure you also know you can IP ban him?

[CHNoodles]

Except that this person uses a wide variety of dial-up IP addresses, and those IP addresses are also used (at different times obviously) by a large number of our regular users; and this person uses a wide variety of domain names for the e-mail addresses, from a site that allows you to create "vanity" domain names for e-mail.

[Erwin]

The bottom line - it is impossible to stop someone from re-registering no matter what you do. So you try to make it as hard as possible. Ban their IPs. Ban their emails. Ban free IP proxies. There's not much more you can do.

For my site, I ban all free email domains. As my staff and I find them, we ban them.

[CHNoodles]

Thank you for the suggestions Erwin.