My mums dog has just started peeing on the carpet for some unknown reason. She's 4 or 5 years old, was previously toilet trained, but has decided it's better to go on the carpet in the lounge.

How can I get the smell out of the carpet? Mum's cleaning it as soon as she finds it, and putting carpet fresh stuff down, but it's still noticeable. I've got a Kirby vacuum so I'll bring it over and clean the carpet, but is there something else we're missing?