We recently adopted a dog named Lena, who has a strong dislike towards cats. Unfortunately, we have a cat named Smokey. We keep them in different rooms and then for one hour a day we take them out and put them together. Sometimes it goes nicely, the cat sits on top of the fish tank while Lena lays down. Other times it's not so nice, the cat hisses on top of the fish tank while Lena barks at her. Like I said though, most of the time the dog gets the run of the house except for our room.
One day at roughly 6:15 I heard a sound that reminded me of our door opening. Our door handle is broken so we have part of a different door on it. To open the door one has to turn the handle, and it's very tiny because it came off the laundry room, lift up and pull in. It is nearly impossible for a cat to do. Yet here I was hearing that sound, that only made the noise when you were opening the room from the inside.
I got up to get more coffee and investigate when I saw the door was open. I ran into the room and quickly looked for signs of her, I grabbed her food and began shaking it and walking around the house. I called my boyfriend Chris to see if he had any insight into where she might be. He directed me to check under the bed. When I looked to my relief she sat under the bed looking at me. I grabbed her and hugged her and thanked my lucky stars. I told my boyfriend and he told me he sometimes sees the handle on the door move at night, but thought nothing of it.
Just a few minutes had passed when Smokey began to hiss at the door! I didn't know what to do except for wait. After about two minutes she sat in front of the door and began to clean herself. If anyone has any information or advice I would love to hear it. I am afraid of what might happen to her if Smokey gets out and has a not so pleasant experience with Lena, but I'm more afraid of what can open our door.
Point is, cats are clever. And some are determined.
I think your biggest issue isn't the door, but the dog. Behavior training should go a long way towards helping the situation. Your local pet store can probably recommend someone, some pet stores have a trainer that works for them. Bottom line you've got a tragedy waiting to happen. Don't sweat the doorknob, it isn't as important as solving the dog/cat issue.