I had the a different situation (kitten and puppy nearly the same age) but let me tell you an absolute truth - dogs eat cat poo and cat food. You can not (in my experience) keep the dog from eating the cat food and/or poo if it is within muzzle range of the dog.
Anyway, try crate training the dog. Get the dog used to basically living in the "crate" (wire mesh open cage). Then the cat can investigate the dog in relative peace.
You can also try the room method where you stick the dog (in this case since it's the "intruder") in a room with the door closed and let the cat sniff the door until it gets pissed (and it will) and runs away. Eventually you let them get used to each other through the door and supervise cracked door visitations in which the dog will go apeshit and try to escape and the cat will freak out and swat at the dog and scamper away about 3 feet and make another attempt to see what the dog is about as long as you are there. You MUST make sure that the dog does not see the cat as a toy or an enemy. Otherwise you will be minus one pet, one way or another.
Ask your vet. Vets know better than online weirdos at least.
PS I'm not lying about the poo thing. Trust me.