So I have a cat and two dogs. My two dogs love cat food, they think it is the best thing since sliced bread, which they also love, but is totally not good for their waistlines. SO, back to cat food... 

Technically, my dogs can eat cat food. Cat food has extra taurine in it, which prevents kitties from developing heart issues or going blind, generally things I try to avoid for my pets. Dogs do not have the same level of requirement as do the cats, so if I feed both my cat and dog the same brand of food (or the same quality of food), you'll notice a price difference. That price difference includes the taurine, but also includes even higher meat content, less bone content, and less fillers, comparatively speaking. That is what makes the main price difference between cat and dog food from the same brand - and all of those items are good to have for kitties.

Again, back to dogs eating cat food... Generally, it's the price difference that stops people from feeding dogs the cat's food. Dogs can have more bone (I mean, they love chewing on bones!), they can have more veggies (dogs are scavengers, cats are obligate carnivores), and again, certain other vitamins/minerals/amino acids need to be higher for kitty health.

So if my dogs eat the cat food, they are totally fine. If my cat sneaks some dog food periodically, my cat will be fine too. BUT I cannot feed my cat the dog food for the reasons listed above that make cat food special. But if my dog needs a special diet, and that special diet is available for cats (like Farmina Urinary formula), I can feed that over some other options that may not have the same quality of ingredients that I prefer for all my pets.

And getting back to keeping the dog from eating the cat food... My simple solution is to elevate it to a level the dog cannot reach. Other solutions involve having the cat bowl in a room only accessible to kitty - by gate, by being the cat room, or by any other means. I have my kitty's food bowl on the top shelf of his cat tree, which he loves!! Since the cat tree is carpeted, I bought some plastic shelf liner, cut it bigger than the bowl area since I add water to his food and I wanted to be able to clean the area. But since he loves his food, he generally keeps it way cleaner than I would, so Go Mickey Blue Eyes!