General Website Security

If the URL is unique enough it is unlikely that a random person will find it but why not add a username and password for added security?

You could add something like this to your .htaccess file to require authentication by a particular user on the system:

AuthType Basic
AuthName "Authorization Required"
AuthUserFile /var/www/passwords
Require User tom

To create the authentication file /var/www/passwords with user tom in it:

htpasswd -c /var/www/passwords tom

(related link)

Here is a related link that claims that unsecured "secret" directories will most likely remain private as long as know one that knows about them publishes their location.