Are there any good services or packages for doing this, especially for RoR? I don't need it for advertising, but for banning abusive users who are able to evade the usual means of detection.
I'd advise not making it obvious they've been banned. Let them submit like normal, and maybe show it back to them like normal, but hide it from everyone else. They might just assume everyone is ignoring them.
We've got hellbanning. It helps but they figure it out pretty quickly, especially in chat. I run a kids site, so we have to be pretty draconian about keeping out bad actors.