Most cats like unscented litter and a private location for their litter box. They also like the litter about one to two inches deep and not a small litter box. Some cats like their litter boxes very clean. Changing the litter type is enough to set a cat off. If a cat is pooping on the floor else-ware might be upset stomach, intestinal parasites. Also, take a look at what's new in your cat life. Some cats with house soiling might have urinary tract disease. Take the cat to the vet for a checkup.
Often the stress level is the root of litter box issues, cats don't deal well with stress. Try playing classical music when you are not at home. Have sessions of play with a toy wand that he/she likes, give your cat a treat, and spend more time with it. If an older cat won't use the litter box, it could be because it's in pain, squatting might hurt, stepping into the litter box might be more difficult.
Professional Pet Sitting Services offered in the Upper to Mid-Pinellas County Area