Good question. If you guys don't want to use a software like DLGuard, my best advice is to keep the download page as far from the root of your site as possible. If you have several different domain names or websites hosted online, it could be better to move the file entirely to a different domain. You can then have your download page link to the downloadable item (even though they are actually downloading it from an alternate location). If you don't have that option, and your site is at:
www.website.com, just make sure that you do not put it at:
www.website.com/thankyou.html or anything close to that.
It would be better to have it deep into the site, ie:
www.website.com/tr/6789yu/htke/889/item.pdf (within many folders).
The worst possible case scenario would be if Google indexes your download page! To avoid that, you can create a robots.txt file and upload it to the root of your site. (ie:
www.website.com/robots.txt) and in that file you should specify which folders you do NOT want the search engines to index. Here is a free robots.txt generator:
http://www.yellowpipe.com/yis/tools/robots.txt/ I think there is probably a simple php code that could also be used to hide/redirect and I will look for this online...must do some research...