When we were kids and our parents would correct us, they always changed the tone in their voice. Their tone would be deep and strong versus soft and sweet. When we correct our dogs, we have to do the same thing with them.
Dogs understand tones and body language better than they do english. Using the right (stern) tone while getting on to your dog will reinforce the correction you are giving. Using the wrong (soft) tone will only confuse your dog or lead him to think everything he is doing wrong is what you want him to do. Always make sure everyone in your house hold is on the same page while trying to correct a dog. If everyone is not, this will also cause confusion for your dog.