It can be challenging to identify the signs of separation anxiety in dogs, but there are a few common symptoms that you should be aware of. The symptoms of separation anxiety in dogs can depend on the severity of the anxiety but may include barking, whining, pacing, restlessness, destructive behavior, and hiding. A dog's behavior issues, like toilet training, leash aggressiveness, barking, or biting, can make an already nervous pet even more agitated when left alone.