I tried to keep the decider parameter at first, but I couldn't get it to work. I'm afraid I don't seem to have properly documented precisely why I couldn't get it work with the decider, though, sorry. Looking back at it, I guess (though haven't tested) that it would be because of the filter in generate_unique_slug - this now needs to access the model itself as well as the slug lookup. I'm not sure if there's a way to have it work with the decider, it would be good if so, as you say, or just have a GenericRelation if you want the unique_with functionality.