Cat scratching carpet, help needed to avert felicide!

[TabithaTwitchet]

Hoping someone can help. We recently had the whole of our house recarpeted (at considerable expense).
Our cat has started scratching the carpet on the stairs - it already looks fluffy and motheaten (the carpet, not the cat) and DH is livid.

Cat knows it is wrong and only does it when we aren't there, so haven't really had the chance to "tell him off" about it (something he usually responds well to)
We have been solving things so far by shutting him in the kitchen at night and when we are out - he has cat flap to the garden from there.

BUT he has just discovered the kitchen door handle, and the fact that he can open the door, aargh. So we can't do that anymore.

Desperately in need of some sort of deterrent to stop him scratching that actually works! We have put his scratching post invitingly near the stairs, and he uses it if we are in the room, but if we aren't in the room he uses the stairs instead.

Help please, feel like weeping whenever I see the state he is leaving my beautiful carpet

For a start I'd be putting a lock on the kitchen door to stop him getting in when there's no-one around to tell him off for scratching.
Then I'd be putting something on the carpet to deter him, such as pepper dust or a repellent spray.

I have an almost 2 year old, so don't want to scatter anything nasty like pepper dust around.
Agree a lock for the kitchen is needed, but what I really want is to be able to leave him on his own in the house without having to lock him up - it is a real pita to have to search for the cat and extract him from whatever inaccessible sleeping place he has found for himself every time we want to go out.

It's difficult with a child around, perhaps you'd be better off with something like sticky paws but I don't know how you could put it all over the stairs.

I did read that using a few drops of something like clove oil will stop a cat scratching a section of carpet. I never tried it because it's not practical for me, but might be worth a try. I'm assuming that any oil would work (e.g. orange, albas, something strong smelling). Obvioulsy if you put oil ona carpet open the pile to avoid staining.