Clever dogs, like corgis, need lots of mental stimulation. A good way to keep them stimulated and prevent them from gnawing on your furniture is give your dog treat dispensing toys. Pop in some treats or dry kibble and let your dog roll the toy around in attempts to get the food to drop out. Or if you have a Kong toy or hollowed bone, smear a thing layer of peanut butter inside of a toy. Dogs love peanut butter and will do anything to get to it.
Example of a treat dispensing toy: