Inherited kittens are never the brightest

Lately, Anne Frank has decided my sofa is the most ideal location for her to start taking her leaks.

I immediately spray it down with cleaner, scrub it 'til the colour bleeds, cover it with pungent lemon air freshener. It doesn't look like piss, it doesn't smell like piss, and unless you read this, you'd never know there was cat piss there at all.

Yet, she'll do the same thing tomorrow. Anyone have any idea how I can break this habit without breaking her neck? 'Cause one or the other is bound to happen.