Although the method of serving an APT repository I discovered when setting up Debian on MacBook Pro 5.2 is sufficient, it is not very robust. Thus I began looking for something more useful for multiple repositories, and which is packaged for debian itself.
The search led me to a post that demonstrated how to configure a
private repository using reprepro. Although that gave me almost
everything I needed, one final bit was required: permission adjustment. As I
use Mathopd, the easiest way to prevent visitors from accessing the
db directories was to restrict their permissions to that of my user alone.
$ chmod go-rx conf db