Never praise or treat if the dog is making any noise, or the behavior will just be reinforced. All of the above suggestions require work on the part of the owner and they will only be effective if the owner is consistent and can follow through correctly each and every time. If this is the case, one can buy one of those citronella collars which spray citronella into the dog's face whenever it barks, or go to a shock collar which will give the dog a shock whenever it barks. The last option is to have the dog debarked by the veterinarian. It is a fairly simple procedure, but does require anesthesia, and the dog must be kept quiet for a few days afterwards to allow for proper healing.
Some vets are better at debarking than others.
Contacting collie or sheltie breeders will usually turn up the name of a good debarking veterinarian in the area since so many of those dogs are debarked.