We tried everything: a gate, she just jumped it , keeping the door closed, the cats would go elsewhere if they couldnt get it, sprinkling hot sauce on it, made the cats weirded out and just made the dog lick her lips more....
What we finally got....so simple and works too!
http://www.amazon.com/Clevercat-Top-.../dp/B0002ZS20I
Hope this helps someone else, we got ours at Petsmart