if it helps, i create an .htaccess file with just the following in and place it in thefolder I want to stop prying eyes looking in:
Options -Indexes (I have attached the file as a zip should you wish to use it)
I then set up a 403 error page - to see this in action take a look at http://www.ybg.org.uk/uploads
I like it because its simple and specific and also the assets within the folder can still be used throughout the site without any issues at all (well none that I have come across)