K.A.
We have an 18 year old cat that we have always had problems with until I made her a litter box of her own, in an area, by itself, and it doesn't have litter in it....it has a doggy pee pad in it. She use to get in the litter box and use the bathroom and then shake her feet like they were filthy. She would step out of the box and use the floor. Until I tried the doggy pee pads, I wanted to choke her. She is 18 years old now and still using her pee pads.
Hope this helps,
K.