I'm designing a web site and I designed an error page with .htaccess so that when someone types in an incorrect URL, it takes them to my customized page. Well, I used server-side programming to make it log the bad URL and check against a database if the there is a good URL matching the bad one. If so, it redirects to that page instead of giving the error. It's a good, well-written script done by me, I'll give it to anyone that requests it.
You see, when they click the back button, the revisit the error page and it relogs the bad URL.