I would buy this to save my grass from my dog. But if my only option is to put it on top of my original grass, then the dog turf will eventually kill the grass underneath. Correct?

If you put our Pet Turf Rolls or any turf roll over grass, it will kill the grass underneath if left over the grass for an extended period of time. If installed temporarily, the grass would not be affected. Once removed, grass would be able to grow again.