I have a bunch of shared libs installed on my system which aren't dependencies of some concrete package but are needed for non-apt-managed libraries I've built from source (like latest SDL, Allegro, SFML, ...) and other software built from source. The problem is that those libraries are seen by APT as unused, and are therefore candidates for auto-removal, and those get mixed up with legitimate unused packages that are free to remove.
Is there a way to mark packages as used so that they are not suggested for auto-removal? My first thought was to build my own metapackage just to hold the dependencies (like for example ubuntu-desktop is), but I don't know how to do that.