Using htaccess to redirect changing site link structures

Catching 404 Visitors

Running a site requires maintenance from time to time, perhaps an upgrade to the file structure too. Even if you’ve not altered the file structure from the original set up, a simple mistake such as an incorrect link in your content, can cause a 404 Not Found error. Unless you’ve set up a custom 404 error page that offers a correct navigation to your main site (which I would recommend too, if you’ve got the option), then you could lose each visitor, a potentially paying customer, when that get that dreaded 404 page and leave your site for good. Also, when a file structure is updated the old files will still be known to the search engine spiders and they’ll continue to search for these files.

She goes on to show and explain some htaccess code and a php alternative to redirect both static links and links including a query string.