I see this A LOT. Have had the same issue myself. Dogs are extremely food driven by nature. I believe you CAN train them to stay out of the cat food but it takes the kind of consistency the vast majority of people just aren't down for. It's frustrating and after all your efforts, it still might not work, depending on the dog.

I think it's easier and fool proof to just put the food on the counter or desk where the issue becomes a non-issue. Many of my clients cats have their food off of the floor and higher up away from dogs.