Well, they more get stuck in infinite voids
... Immagine, you can navigate to a future date in the calendar, so what's to stop them from going to year 4098+... You really need to block them from certain threads locations...
robots.txt:
User-agent: *
Disallow: /files/texts
Disallow: /forum/ubbthreads.php?ubb=calendar
Disallow: /forum/ubbthreads.php/ubb/calendar
Disallow: /forum/ubbthreads.php?ubb=showday
Disallow: /forum/ubbthreads.php/ubb/showday