Dogs may chew drywall, furniture, climb fences, dig, have accidents due to stress when left solitary.
Destructiveness
Loud distressed vocalizing while owner is gone signals isolation anxiety. Recording helps determine if barking occurs the entire time.
Howling
Some anxious dogs lose control of bladders/bowels when alone. Separation elicits a panic response.
Defecation
Excess slobbering or heavy anxious panting leaves telltale signs of stress while you were away.
Panting
Dogs may avoid the usual excited greeting or not want owners to leave.
Depressed Greetings
Dogs track owner's movements anxiously before being left. Pacing, trembling continues in solitude.
Trembling
Breaking out of crates, enclosures or even through windows indicates extreme distress when alone.
Escaping