Maybe spawning animals on such territory would be better. Having no-one's land inside your borders, just because there are some, e.g. forests with game, is a bit too harsh, I think.How's this for an idea?
An improvement, that you can build in domestic or neutral territory. While a tile has this improvement on it, it will always be neutral territory.
Wild animals could move around such terrain, even in cultural borders.
That potentially would lead to increased turn processing times.