It's a fact, dogs like to chew. They will chew on almost anything at any time. Needless to say, this is not a favorable behavioral characteristic when it is coupled with the furniture or shoes. However, dogs' tendency to chew can actually be harmful to them, even fatal, if the chewing occurs on electrical cords.
There are several ways that dog owners can go about keeping their dogs from chewing electrical cords.
The first method is the easiest and most effective way to discourage repeated attacks on cords. Hide them. Physical barriers provide an easy and effective means to ensure that your dog doesn't chew for the last time. Make sure that all electrical cords are safely hidden behind immovable furniture items. This approach should be employed for all reachable cords, plugged in or not.
The second method works reasonably well if cords cannot be hidden from your dog. Bitter apple or bitter lime spray applied liberally to exposed electrical cords will serve as a deterrent for most dogs. It needs to be noted that some dogs' chew instinct is so strong that they will chew regardless of the spray. Bitter apple and bitter lime can also be used on other surfaces (test colorfastness before using!) to discourage chewing.
The last method is careful training. Dogs can be conditioned to not chew on cords by the use of behavioral modification training. While this method is very reliable for some dogs, it may be iffy or a complete failure in others. While behavior training is very important, coupling it with another deterrent will increase your success rate exponentially.
It is also important to note that while you are attempting to encourage your dog not to chew on electrical cords, you should be providing items, whether toys or specially designed dog chews, for your dog to chew on. A dog is less likely to chew on things he should not when he is provided ample opportunity to do so on approved items. Things that are appropriate for your dog to chew on include: rawhides, pig's ears, sturdily built dog toys, etc.
And lastly, be patient. If you find yourself losing your patience with your dog, walk away and cool off. Remember, chewing is a natural instinct for your dog. Punishment will only serve to make your dog afraid of you and potentially aggressive when you try to redirect his chewing. Reward him for appropriate chewing.