Much like with humans, obsessive compulsive disorder in dogs is characterized by the uncontrollable repetition of bizarre, out of context behavior. This behavior can be literally anything and is directed either at other animals or humans or even at inanimate objects such as food dishes or a piece of furniture. In the least severe cases, your dog's disorder might manifest through something simple like pacing back and forth, or hiding in a particular spot for seemingly no reason. At other times, it can become more problematic such as when they begin to bark at "nothing" for hours at a time, or destroy your or other's property with no provocation. In the worst cases, your dog might cause serious problems by turning its frustration against itself. In many cases, this might manifest as destructive behavior such as the dog compulsively chewing on its own foot, resulting in infections and problematic lesions. Dogs that exhibit obsessive compulsive disorder are often mistaken as being overly aggressive, but in fact this is not usually the case. They are simply acting out in ways that are perceived as threatening by those who can't understand the dog's motivations.
Generally, Canine Obsessive Compulsive Disorder is thought to stem from one of three causes: stress, anxiety, or boredom. Diagnostics are handled differently in all cases. Once the disorder has manifested itself through behavior, possible causes are analyzed and narrowed down. If something is identified as causing significant stress to your dog, then his or her disorder is likely caused by that. If there's been a recent drastic change in your dog's lifestyle, including the possibility of separation anxiety, then this is a very likely cause as well. Lastly, dogs who are insufficiently entertained or exercised will often develop obsessive compulsive disorder, so this cause must be analyzed as well.
In the case of obsessive compulsive disorder caused by stress, medications are administered to your dog in the hopes that they will not only reduce stress, but also curb the likelihood of any aggressive outbursts. Anxiety-related cases are treated by identifying and eliminating the underlying cause of the anxiety, be it another animal or insufficient attention. Cases related to boredom are the most easily dealt with and usually only involve becoming more engaged with your dog. Exposing him or her to lots of activity, taking long walks, playing intensive games and in general just expending as much of his or her energy as possible will usually be enough to avoid the feelings of pent-up frustration that drive the animal towards misbehavior.
In many cases, however, you might find that there is no real "cause" for Canine Obsessive Compulsive Disorder, and that they've simply inherited the tendency as a matter of genetics. If this is the case with your dog, then treatment of the disease is simply either learning to deal with the strange behavior he or she is manifested, or attempting over time to correct it through behavioral modification techniques if the problem is severe enough.