You will lose a pound if you burn 3500 more calories than you take in. This is one of the bottom lines in weight loss but whether or not you are actually burning 3500 calories varies from person to person with the same activity.
A dog can survive without eating for 14 days, procided day wouldn't be in good shape and health.
Dogs die after 3 days with no food or water. They are in trouble after 24 hours without it, so if you're dog is regularly going without for 12 hours, this will end up being detrimental to his health, probably starting with his kidneys. Best not to risk it - try training techniques to correct the situation.