Normally server side scripting languages like PHP and Perl doesn't make their source easily available unless your web server is misconfigured. For example, if its set up with improperly defined MIME types then its possible that users may unwittingly download the source code to your scripts.
To avoid this, you may want to look into setting read/write/execute permissions on the files themselves especially if the files are only meant for a select few then you can probably set them with r--r---- permissions. (read owner, read group, no access anybody)
Another thing that you can do is to give your DB source file definitions obscure names. That may help. Finally you should disable directory listings in your webserver by either include an index.html that redirects any access to the directory to your main page or consulting your Webserver manual for assistance on this area.
