Introducing...BendyLatch! A 3D-printable latching mechanism to keep large dogs out of any room while still letting cats come and go as they please!

This mechanism is very simple - hang it over the doorknob, then gently bend the latch such that the pin rests in the strike plate of the door frame. You should then have a ~4.5" gap that even the chonkiest of felines can squeeze through, while keeping those large K-9s out of the litter box, food, or whatever private space your cats like to enjoy by themselves.