I understand your suggestion but if this digging up old threads is such a big problem (to me, personnally, it isn't but to each his own & I'm not a mod
), I really suggest following Gaelen's advice and try and get old posts automatically locked.
This will keep newbies who don't know our group behaviour/etiquette from doing it as well...
I found this link:http://www.phpbb.com/community/viewtopic.php?f=72&t=1908995
... but that might be a bit of a dirty hack (directly fiddling with the database storing the posts. There might very well be some kind of setting or plugin that can be used to automatically lock posts.
If you want to discuss further, I'd be glad to continue via PM..