Are your dogs home alone all day? With little or nothing to occupy their time?
Many people leave a radio or television on for their dog when they leave. The "white noise effect" does seem to have a soothing effect and thus may have some redeeming features. Any lilting/melodic sound (not "heavy metal") or even just background music is probably better than the sound of silence or a clock ticking on the mantelpiece. Most animals seem to prefer seeing images of other animals or nature programs.
Another tip is to exercise your dog before you leave. My dogs go for daily walks both to calm them, and also so they can "do their business," so the exercise has a dual purpose.
Exercise generates serotonin in the brain and thus has a calming and mood -stabilizing effect on man and pet. A dog that has had a good run for 20 to 30 minutes before the owner departs will be less anxious, more composed, and prepared for a little R & R in the form of a good nap.