
Hi Dahn, I agree with @Callender Girl...you might not be seeing predators but they are out there even in the city.
While it might not be an inexpensive solution, maybe a dog kennel would work for a couple chickens...something like that would be easy enough to cover. And you could bury a "skirt" around the bottom to deter digging predators. Maybe you could even find a used one through CraigsList? For example:
However you proceed, best of luck!