
I've always had to be careful about cat food, as if my dog manages to eat any he scratches non-stop for about 12-24 hours afterwards (makes you wonder what they put in it! lol). When mine was a kitten I managed to fix up a small dog crate so the end door was firmly fixed open at cat-width but not dog-head width, and she was fed in there. She had another small crate similarly fixed up for her litter tray (cat tray crunchies = yum yum for dogs). Might be an option if you are finding things difficult.
Now she's grown up she's fed on worktops, or on top of the freezer in the back porch, well out of dog's reach.
PS: Much of the time she is now fed raw, so if dog does snaffle it there's no repercussions and she's a lot heavier and fitter than when fed solely on commercial cat foods.