I had the same issue with my Bella. I cant leave food down either. I just have to spend extra time with Piper and her food to make sure Bella doesnt eat it.
Have you seen those break-fast bowls. there is also this other thing like a big metal ball that you put in their bowl. They have to roll the ball to get under it to get the food. It really slows them down.
Maybe someone will have some good ideas for us both!!