Here’s a novel tactic I haven’t seen discussed here on Meta yet:
With regards to spam, I am fortunate enough to run a forum where Google indexes posts in a matter of minutes. This does have its own issues though in that it attracts spammers who realise they can get links on Google within minutes!
What I’ve had to do on this forum is make it so that for non-registered users (and therefore Google bots), posts from user accounts less than 24 hours old are hidden with the message “to prevent spam, this post will be invisible for 24 hours” or something like that. It could use some work as ideally you would hide a whole thread for 24 hours if the user was <24 hours old, but it has effectively cut spam right down (spammers must have realised they’re fighting a losing battle there) and gives moderators a little time to deal with spam.
Strangely, when I suggested this idea to the popular forum developer concerned, they weren’t interested - I’m not entirely sure they understood how effective it was but I would highly recommend it as a simple, effective tool in the anti-spam arsenal! Plus, to my knowledge, none of the other forum developers have tried this approach, so it’s still unique at the moment