A litter box can be clean and still be difficult for a cat to use if it is noisy, trapped in a corner, or guarded by another animal.
Choose accessible locations
Place boxes where the cat can reach them without passing a frightening appliance, slippery staircase, or competing pet. Avoid putting food and water directly beside the box.
Provide options
In a multi-level home, a box on each commonly used level can improve access. In multi-cat homes, separated locations are usually more useful than several boxes lined up together.
Keep the route open
A timid or older cat may avoid a box if another animal can block the only exit. Open spaces or boxes with more than one approach may feel safer.
Sudden litter-box avoidance can have a medical cause. A veterinary examination is especially important when the cat strains, produces very little urine, cries, or visits the box repeatedly.