Lately, I've been creating protocols that are meant to be the interface for some kind of entity, such as "user", "utility", "configuration", "auth", and so on.

Lately, I've been creating protocols that are meant to be the interface for some kind of entity, such as "user", "utility", "configuration", "auth", and so on. The logistics of that are to use defgeneric for the protocol interface, defmethod in the same package, but can be over-ridden with a more specific defmethod in another package if necessary. I still export regular functions too, but I look to the defgenerics as the main entry points for a particular package. To (sort of) enforce some separation, I try to keep these packages self-contained in their own system (defsystem). I mean, it's one approach, but my advice would be to take some time to come up with what would work for your appication and CL is flexible enough it can probably support it.