Thumper at her previous home was the only cat. When she came to live with us, I noticed she would poop and run so to speak out of the litter box and leave her stuff on covered. Watching Butterscotch bury his stuff she caught on and now covers it.

Not sure when both animals won't bury what you would do. They got the digging part right. Maybe there isn't enough litter in box to cover? or too much litter? This is a stumper .