I have a border collie/greyhound mix that is obsessed with moving beams of light, flickering shadows, etc. She has become very destructive because she claws the furniture where this light appears. She has trashed the upholstery. I can't seem to make her stop. She is very intelligent but very stubborn.
My dog will growl and bark at dark spots on the wall, similar to your problem. When he does it, I either take him on a walk, or I have a laser pointer and he will chase it until he is totally exhausted. Either way he ends up tired and forgets about the wall. For my own dog I see it as a sign that he is restless and needs to burn some energy.
Try to distract and tire your dog with other activities like walks, frisbee, etc. if she starts attacking the lights and shadows. The laser pointer might not be a good idea because it reinforces the chase behavior, which in your dog's case is a destructive behavior.
Laser lights can cause obsessive compulsive disorder. Its a very tough behavior to break and deal with. You will need to be really patient and you will need professional help in doing so - a behavorist or trainer.
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