This is a question that we often get from sitter and owners who work with Rover. Help the community out by answering them in our forum!
Option one: Some people like the top entry litter boxes like the Clevercat Top-Entry Litterbox if you dog is short. If you have a taller dog this might not work.
Option two: In a previous house I used a closet under the steps as the location for our cat boxes. You can put a kitty door on the closet to keep the dog out or make a wall entry (this may be cheaper to cover when you move or sell your home) and use any type of litter box that you choose.
Option three: If you have a smaller cat you can turn the door of a covered litter box to the wall with a wide enough distance from the wall to the door so your cat can shimmy in. I wouldn't suggest this for older or larger cats as it will be uncomfortable for the kitty to get in, but for smaller kitties it works like a charm.
Unless you have a very determined dog option three is the easiest and least expensive. Option two is my favorite as it keeps odors and the litter box safely out of view.
One possible solution is to use a high-sided tub (Rubbermaid Tote or similar) as the litter box to prevent your dog from being able to get to the cat poop. Another option is to put Forbid powder in your cat's food. It will change the taste of the feces, so your dog is less likely to want to eat it.
Poop eating is most often a behavioral thing, rather than being due to a health issue, but it can't hurt to make sure your dog is on a good quality food.