Automatically lock threads that haven't been posted to in more than 2 months

I see this all the time. Some newcomer finds us on Google and replies to a 2 year old thread and all it does is clutter up the threads list with irrelevant junk. And now someone is intentionally going to all old threads and bumping them...

So I propose to lock threads that haven't been posted to in over 2 months. Users have the ability to message staff to unlock a thread if they absolutely have something to contribute.