Cats - claw sharpening on carpet

Question
The cat from next door is trying to take us over.  He is a cat who spends a lot of time outside, but also has indoor accommodation with his owners, who feed him well but are not often home.  
Whenever he gets into our house, beyond the kitchen, the first thing he does is sharpen his claws on my hall carpet!  He is making a complete mess of it and I always chase him out when he does it, but I am wondering WHY does he do it when he has access to trees etc. outside, and probably also a scratching post at his own home?

Answer
Valerie,

My guess is that he loves the feel and the smell of your carpet. He may be leaving his 'mark' at your house. It is also a feel-good, make-myself-at-home response to being in your house.

Try using a water spray bottle when he does it or slap a rolled newspaper loudly against something. That way he will associate scratching with a loud noise or water which he won't like.

If he is tame enough to pet and handle, I would trim his claws. Here is an excellent site that gives you photo instructions:
(copy and paste, or type, the whole link into your address bar:)

http://www.cat-world.com.au/catclaws.htm

I hope this helps.

Tabbi