Store database password outside of public_html folder

Hi All, I've been reading on the internet that is most secure to store your database details outside of the public accessible folder. I am a bit stuck on how to do this. I've got a folder "db_details" that contains the file "dbdetails" which contains the database login info. I normally include this file in any page requiring database connectivity e.g. include_once("db_details/dbdetails.php") How can I now set this up so that the folder/files for the database are stored outside of the public_html folder ? thanks