IMO, an autolocking feature would be an excellent one. If it existed, I would personally already have it turned on. tyme added a "are you really, really sure you want to post in this very old thread" question to old threads that a member has to check off in order to reanimate them. That helped a lot, but a handful of old threads pop up every week.
While hogdogs brings up a very valid point, I feel there is an obvious and very easy solution.
Doing a search for info is always a good practice, and chastising those who don't is often valid if done in a polite manner. However, there is no need to resurrect a very old thread just to add your own flavor of the question. Either your quest for info was completely satisfied by the info in the old thread, or it wasn't. If the latter, then a new thread should be started with a specific question. The old thread can and should be linked as a reference. But, bringing back the old thread with a question at the tail end is both confusing to the general membership and doesn't help the person trying to find new info. Invariably members will start out answering or commenting on the first few posts that are now several years old (and the OP is often not even visiting our site any longer).