We bought a leather sofa from Ikea and only had it one day, and one of our two cats went to town on it. He literally hung on the side with his claws. Even pushing him off didn't deter him. I think it is the smell of leather. He made such a bad job of it within a couple of days that we had to put a throw over it. Heartbreaking! However, since moving we have been able to position the sofa so that the affected side is towards the wall so it doesn't look too bad. We are now able to shut the door that the sofa is in!
I once saw a brilliant humourous birthday card which had a picture of a man with his cat on the front. The man had just had the cats claws taken out at the vets and he is looking very smug. However, there is a thought bubble coming out of the cat with a picture of the cat holding a fork ready to stratch with that!
All you can do is cover the whole sofa with a heavy duty cloth, tucking it right under the feet etc. whilst you are away. On a longer term basis, there is a furniture polish spray on the market which smells of orange peel which apparently cats hate. You could try giving that a spray on your sofa. Check first that it is suitable for leather.