Poopy Problems !

Hi there, I'm wondering if anyone has any suggestions.......

Whenever Kiki uses her litter tray, she doesn't bury it. She does try to but usually she just scrapes outside of the tray, occasionally she manages to bury it but not very often, both of my cats like to stand outside of the tray while they are burying and just stick their paw over the side. Any ideas on what I can do ?

Not only does Rosie dig to China, but she hardly ever covers her "packages", but if she does she stands outside the tray and gives long sweeping strokes with her paw that sends the litter flying all over the place

When she doesn't cover it though Sophie jumps on and covers it for her with quick short flicks, and i often wonder if she's thinking "She's older and wiser than me so should know better!"