The lastest trend to prevent cats scratching is to glue vinyl nail caps onto the trimmed claw. Apparently invented by a vet(!), this callous technique disregards the functional purpose of cat scratching and the welfare of these cats.
Scratching has a variety of functions for cats: it enables them to scent mark using the scent glands on their paws; it exercises the ligaments in the paw; and it also sloughs the outer claw. There are 2 serious consequences to preventing a cat from scratching:
1) The cat cannot flex and excercise its paws to their natural extent; and
2) The outer layers of the claw, which should be sloughed, will toughen and thicken the claw, resulting in an oversized claw that is painful to retract, walk on, or trim.
If you are looking to rescue your furniture from cat scratching, there are plenty of alternatives. Cats like a vertical thread to scratch, which is why they often ignore their scratching posts in favour of wall paper or the sofa. Commercial scratching posts often have rope wrapped horizonally around the post, which is not easy for cats to get their claws into. Try getting some hessian sack-cloth material and wrapping it around the scratching post to make it more appealing. Or buy some carpet cut-off and tying it around the post, underside out. Put your cat's paws on this new, improved surface and fake a scratching motion for it; this puts the cat's paw scent on the post so that it knows where it is supposed to scratch, and introduces it to the new favourable substrate. You can also sprinkle catnip on the post - a 'kitty cannabis' bribe for scratching there! By placing double-sided sticky tape on surfaces that you would rather your cat didn't scratch, e.g. on the corners of your sofa, you will make these surfaces less appealing to your cat - cats don't like the sticky feeling on their paws.
If these techniques do not work, please consult a behaviourist rather than resorting to unnatural quick fix methods, like the vinyl nailcaps. I know of no animal welfare charity that endorses this - it is far kinder (and less of a hassle in the long run!) to redirect a cat's desire to scratch than to stop it from performing a behaviour that is as natural for cats as eating and grooming!
I have a Masters degree in Appied Animal Behaviour and Animal Welfare and have been working in the animal welfare industry for a number of years. These opinions are formed not only from personal experience but also from consulting with Veterinary Surgeons and Veterinary Nurses in my field.