Kitty Overlord Domain

Ok, we've had them for quite a while now, and...well....sure, they KNOW where to use the bathroom, yet they like doing it on carpet sometimes. So any tips on potty training them, to make sure they never ever go on anything carpet again, or is it common for it to happen, where they sometimes like to use the carpets?

They also bark whenever any door opens, so is that common in dogs too?

Yeah, I'm probably gonna be asking for pet help for a while.....at least until I graduate.