I don't want Perl Monks to become something like another site*, but on another site, there is a time limit while your message is kept, something like 15 days.

While I think that the time limit is too restrictive, IMO a 3 - 6 months limit could be considered coupled with an option to preserve certain messages longer than that timeframe - the important stuff.

This measure would of course merely complement other solutions mentioned above, by Tanktalus and others.

* Yes, /.