I can't imagine a bike getting stolen from there, even if unlocked. I would go with a cheap cable-lock. But if you will venture out to the city for errands etc from there, then as others have suggested, keep whatever heavy-duty locks you want in the cage. Since they're there, you might as well use them, and you can take them out on errands, but most of the time you won't have to lug them back and forth to home.