Here's the thing: the spammers are no longer just bots. A lot of them go through the verification process, which means it's a real person. If we put such steps in place, they would still get through.
We had one who was rather clever. They would make posts (not just topics) that were generic, but almost fit the topic at hand. Then, one of the characters (I remember one being a period) would be a link to their website.
Sadly, the best option truly is just to hit the report button and have one of us do a ban.