If they are barking while you are getting the food ready just walk away and don't give them anything. Come back in a minute and try again. You might want to start this on a weekend off so you have some time as the first few times it may take a while to build the association. When they are quiet they get the food. It is just that simple. Be consistant and firm. Don't say anything just walk away. When they get quiet go back and try again.