Why don't you moderators delete threads that are "going nowhere" instead of locking them? If you lock a thread or close it, the post stays on the board and not only remains an annoyance, but takes up space of other more relevant threads, which will be pushed to the next page when the number of useless, closed topics becomes great enough. I don't want to tell you how to do your job, but I moderate on another forum and have found this method to be quite useful.