If you want foolproof then you need to remove the root of the problem, which is your hard water. Install a water softener and it will remove any built-up limescale in your system, and of course prevent future build-up.
What we do with surfaces that don't hold the liquid is soak kitchen towel with it and use that. Haven't tried in the toilet but I'm thinking if you do similar with the descaler and wedge it under the rim that could help. Obvs wear gloves and remember to remove it before flushing. Or just use the Harpic in the black bottle as suggested up thread, it sticks better than most.
I've tried Viakal, the only way it would work would be to physically stuff something up there to stop it running away. Ahh, maybe that's an idea...to cut up some sponge or cloth and soak it in viakal and jam it in?
Will try the Harpic black and the Parazone block, thanks. Not together obviously if one contains chlorine!
don't use spirits of salt. will take the enamel off your loo and make it worse. ask how i know I use the black harpic toilet cleaner. its really good at getting rid of limescale as it sticks to the sides etc. Best thing we've ever found for limescale, in fact.
Whatever sort of limescale remover I buy it just dribbles away before it gets a chance to dissolve the build up. This has been a lifelong problem of mine, being unable to clean this area. I even bought a pumice stone but its too big to fit under the rim
I'm even tempted by sprits of salts but I have no ventilation in the bathroom. And surely it would just run down without dissolving anything wouldn't it?