I sympathize as my senior Lily (gray) will also poop outside the box yet always pee inside . . . I think it is due to constipation coupled with her impatience. Sometimes she will leave a little poopy in box, and then I will find a bigger one out on the carpet somewhere . . . this happens maybe once a week. I mix Lactalose (from vet) into her wet food at each feeding to help things move easier for her, but it is not completely resolving the problem. I'm just thankful my old gal does not have the runs on my carpet!