When we first got Killua, he was great at covering up his pp and doodoo!

But now it's like.. sometimes he does, sometimes he doesn't, and I'm unsure why he's 'getting lazy' with covering his stuff up. He has a giant litter box and I fill it up a good amount for him to scrape around in but.. what can I do to encourage 100% coverage all the time? I live in an apartment and any instance where he DOESN'T cover it, the apartment smells rancid. I have to constantly check to make sure he's properly litter boxing. He gets his box cleaned twice a week, complete litter change every other week.

Honestly, if this is the worst thing your bengal ever does, you're lucky. Mine does cover up his waste in the litter box. He does not when he pees while on our walks. He just squats and goes and walks away.

I would try a different type of litter. Some cats do not like scented litter. A lot of cats don't like pellets either. It actually is instinct to cover their waste regardless. So the reason he isn't doing it -- there's an issue there. I know that cat poop can smell to high heaven. I always clean Raiden's waste right after he does it -- except overnight when I might find two clumps in there in the morning.

If mine didn't cover up, I'd be fine with it since at least he is using the litter box.

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The little monsters 3

What a cat , particularly male cats big or small, do with their poo can tell you something interesting.
Many years ago in my silly days I was looking after a young male leopard who had been hand reared but had grown and was time to move on to the big house.(zoo) I was basically the pooper scooper man and water bowl checker. He was just a big playful kitty cat who loved company.
One morning I come to clean his cage and found he had pooped right in the doorway where you step into the cage.
i thought, stupid cat and shooed him in the containment room and cleaned up and didn't think much of it.
Next morning the same but this time the looks and feelings I was getting off the cat gave me the creeps. Wisdom stepped in (at that age even..lol) and I got the keeper and asked whats going on. The keeper red flagged the cat and said I am to have nothing to do with it anymore. Pooping in the doorway where I regularly entered the cage the Leopard had issued a challenge over me entering his territory. The keeper said if he had got out of his containment that day he probably would have killed me. Scary!!
With our cats living indoors and having regular meals on time and a dream life, a male cat in his prime of life and full of health without having to think of survival as in the wild and a lot of empty space in his head can decide to upset the pecking order in the house.
One sign of this is he stops burying his poop in the litter tray. He wants it out in the open and stinking the place out.
He is proclaiming to the world he is king of the castle and this house is his. Next step he will poop on or under your favorite chair just to say you are second place to him..
Simple way to fix this is to put a bit of insecurity in his life and make his dinner an hour late or half the amount,,shake up his tree a bit and the poop will start being buried again and this might never happen again.
Just something I have seen and experienced with cats big and small.
They always thinking and planning..that why I enjoy them so much.

Big wild cats are scary creatures and extremely territorial. I am happy nothing bad happened to you.

A lesson learned.
Decided my ambitions to be a zoo keeper expired not long after that..went back to school and thought that safer than being eaten by something one day.