My 2 year old chihuahua keeps eating cat poop despite being fed well.

Hello everyone,

my 2 year old chihuahua keeps eating cat poop. I clean the litterbox everytime my cat uses it while I'm awake. She also poops while I'm asleep and burries it so well that I don't notice the smell until my dog gets a bite of it. Idk what to do. I can't block off the access to the litterbox since I live in a small apartment and the door to the hallway has to stay semi opened. I thought about buying a top for the litterbox but my cat absolutely despises that, it literally scares her and she ends up pooping outside the box.

How do I solve this problem? It's disgusting and I'm currently deworming both of them since I think my cat go giardia from drinking out off the same glass as him.

I heard it's a chihuahua thing and that it doesn't always have to be caused by vitamine deficiencies.

What do I do? I'm open for all kinds of tips.