Thanks everyone! Kind of helps a lot to know that I'm not the only one dealing with this "smelly problem".

Right, the couch is ruined, and I 've replaced the "seat" by a new mattress now which I have covered with synthetic leather so I have only to wash the blanket on the couch when another accident happens. I got a third litter box for Luna and put one of her boxes in another corner which she seems to prefer. She also gets a Bach flower treatment now. Little accidents still happen, but not as often as they used to.

Even though everyone thinks it's a protest thing, I had her urine checked at the vet's today and they found out she has a bladder infection and struvite crystals (see also http://petoftheday.com/talk/showthre...433#post338433)
, so she's also getting an antibiotic treatment now. Hopefully this will help my little girl!

Kirsten