Simple design to let the cat in, but keep the dog out. Our dog has an appetite for cat litter and it's associates. Instead of replacing the dog with one of more dignified tastes, I built this simple wedge to keep the big headed animal from entering the “cat's room” (the room formally known as my office). The design assumes you have a carpet or rug under the door for it to grip onto. The wedge is 24.5 mm tall (about an inch) 42 mm wide and 157 long. This is the 5th iteration I have done and works the best so far. You may want to sand it just a bit on top so that it does rub to hard on your door bottom.