Environment matters more than training
Because the instinct to use loose, diggable material is already built in, most litter training problems are actually environment problems, the wrong litter, an inconvenient location, or a dirty box, rather than a cat that needs to learn a new behavior.
Nail care is worth building into the same routine
While you are setting up a comfortable litter routine, it is a good time to build a regular nail-trimming habit as well, since both are easiest to maintain when done consistently rather than only when a problem shows up.
Frequently Asked Questions
Can multiple cats share one litter box?
It is possible, but not ideal. Sharing a box can be a source of stress between cats, so the generally recommended setup is one box per cat plus one extra, placed in separate locations.
I keep changing the litter but my cat still goes outside the box.
If it is not a litter or location issue, a painful condition like cystitis or bladder stones that makes urination uncomfortable is a common underlying cause. If the problem persists, a veterinary exam is a more reliable way to find the cause than guessing at home.