There is another option: delete (archive) all pages deeper than level two. Logs, Piwik or Google Analytics will confirm level three is NOT read and all those pesky dead links will never bother you again. (Any single items at deeper than level two can be moved to level two, replacing level two stuff that is not read.) All links that are left should be to your site anyway, but if you must reference external sites, perhaps collecting these on a single page ordered into topics with suitable headers makes managing the links easier? People seldom use links because they are often broken, so they choose to search first.