The first litter box we had for him ended up being too small. He would go through the motions of burying his poo, but he'd be halfway out of the box when he did so. Getting a bigger litter box fixed the problem.
I also got a Litter Genie. I've never had one before, but it's fantastic for odor control. Can't recommend it enough.
Every day when I scoop the box, Tarquin comes to investigate and/or get in the way, and seems very confused about why I would possibly want to save his poo in a little box.

