Selective pet doorstop

We needed to prevent our dog from entering the room where the cat litter and food is located. So I built a doorstop that firmly keeps the door open so that the cats can pass, but the dog not, even when she pushes with all her force.

I wanted this doorstop to not alter the door, nor the frame, nor have to drill holes in the walls. It also had to be easily removable and put back into place.

Obviously this is tailored for our door and pets, but it might be helpful as a starting point for othe