Not burying poop despite attempt

You might want to consider a top entry cat box or an automatic sifting box such as Littermaid.
http://www.clevercatinnovations.com/(S(exvzat45qfcwzq55ui1ut245))/top_entry_litterbox_about.aspx
The top entry box might give her a better chance at covering. You could make one with a big plastic bin.
Cats usually learn this behavior from their mothers so if they came away from mom early or she wasn't good at covering then they may just not have learned it well.
I find that food with little fish or milk products in it makes for less smelly stool.
You could try adding odor absorbing crystals to the litter you use but that seems to me to be more about urine odors.
You could see if she was better with a different litter. But I think its a learned behavior and she may never get better at covering.
Hope this helps you!

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Thank you very much for your suggestion. I don't quite understand why top entry box would give her better chance of covering: it is not that she would run off after pooping, but she is already spending a few minutes each time trying to cover it, but wrong spot. And side entry is necessary to make the box a bit more roomy: they often go with their head sticking out of the box.

Nadya pretty much grew up with Tatra as a sort of role model (their mother disappeared when Nadya was 2 weeks, Tatra was 8 months: I suspect that coyote ate her), but now she covers completely after starting 100% indoor life a month and half ago.

Thats my thought - she could be far away while trying to cover as she sticks her head out.
If you don't need the floor mat you might be able to make a top entry box a bit larger in size. Just put the matt on the top lid to catch litter tracked out.
Sounds like Nadya is a quicker study than Tatra on how to keep things cleaner.
Maybe a self cleaning box would resolve the problem for you.

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Actually when she is digging, she is digging the litter, about 2-3 inches away from her poop. She also digs on the litter mat as well at the end. But she does spend a lot of time digging around her poop: just throwing litter to wrong direction. Perhaps you are right, Nadya is just quick, and Tatra may need more time.

In fact the current litter box is the biggest one that can squeeze in the current place: between toilet and bathtab.
And I am actually very afraid of top end litter box because when they jumps in, if there is a poop, they end up stepping on it, because they can't tell where they are landing on.

I am very sorry that you aren't getting paid, I am waiting for more people's suggestions, more oriented toward Tatra's eventual covering poop, though actually now I'm not sure how the system works.... I thought that as long as it is unpaid, the problem is not resolved yet, and perhaps other people have opinion....

You can try a finer grain litter to see if that helps. If she can move it more easily and has to move it more carefully that might work for you.
You might want to see if a week of having the litter box open would let your less astute girl learn better how to cover the stool by seeing her sister do it.
You may also want to consider finding a spot for a second box as she might not want to scratch up used litter to cover her stool and so be scratching to far away.
Because its a learned behavior how long it will take for a cat to figure it out varies. Some never do. Thats why a littermaid type automatic box might work.

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Thank you for your reply. All you suggest come with some sacrifice (such as bearing with possibly more tracking mess, or having to be extra careful when I take shower etc), but I guess once she learns, perhaps she will keep it even if I change the setting. I guess I'm going to start with talking off the hood. Since nobody else seems to post though it's been almost a day, I will accept your answer. Thank you very much for all your help, and I am sorry for late payment.

Thanks for the accept. I know its not an easy solution but if it works it will be an improvement for you!

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