XF 1.5 Possible to auto lock a topic?

I have a couple of jokers who like to go back and bump long since dead topics. I'd rather not prune the topics because I have some hard core members who like to search and link back to topics. Is there a way to auto lock a topic after a specific period of time?
How often do they do it?
Not enough, yet, to where I want to make it tough for them to post, but I can see them doing it more just for fun. This is a pretty small but active forum. Most of us know each other. Odds are if I lock the topics they've bumped, they will do more.
I appreciate that. Actually, I'd like the others to see they're being moderated. :)

That's kind of group we have.

It's a private set of boards among a larger set of boards. It's not an over riding problem. Just trying to be proactive. I'm not really trying to moderate users, just topics without going in and doing it manually. I think IPS has a timing mechanism to locking topics, but it could also be purging. I don't really want that either. For those who can wrap their head about the Xen API, my guess is it would be an easy add-on to automatically lock a topic after a certain period of time.