Yes, quite common actually and you need to put a stop to her behavior, it is obsessive and not healthy at all. First off make sure this dog gets enough outside walk on a leash time, 45 minutes would be good. If you can find a dog park or play mates for her, and let her play for a half an hour or so the better. Usually obessive behavior is because they dont get enough stimulation or there is something they dont like, or a combonation of the two. The second your dog starts the unwanted behavior, tell her to leave it, and replace what she is doing with a toy or some other interaction. Take her away from the environment where she is barking. In case you are getting no where with this, fill up an empty soda can half way with dried beans. Tape up the hole and when zshe starts the barking, shake the can at her, tell her no and remove her to another room, while she is in the other room, get a toy or ball out and start playing with her. Let me knokw how it goes. Should take about a week if you are vigilant, for her to stop the unwanted barking and oseesion. PS - No more playing with the light pen

Shelties can get bored very easily and they need a lot of stimulation . . . not just attention. Instead of lots of walks, take her on a couple of really long walks. She needs to get tired out. I don't find a dog park to be the best place for my shelties because they tend to try to herd all of the other dogs in the park. However, they do like to have playmates or companions. Have you considered a second sheltie? The behavior of my 1st changed (for the better) after we got our 2nd. Another option to consider is agility training - gives her something constructive to do, training is involved so she's using her incredible brain and it's another way to interact with her. Good luck. Shelties are awesome (but I may be a little biased).

Any kind of herding dog, esp. border collies (I know from experience) can get neurotic if they don't get enough exercise.

Thanks for the input. I don't think it is a matter of not getting enough exercise. We live in the country on 5 acres. My husband is home with her during the day. He tells me he takes her for at least 2 walks a day. We usually go for a walk when I get home from work. We live on top of a hill. It takes us 30 minutes to go to the bottom and back up again. She is also running around chasing bunnies and birds and "helping" my husband during the day when he is outside working, which is most of the day. She gets a lot of attention, but maybe not enough mental stimulation. I would like to do agility training with her. She would be great at it. The breeder told us she never let the puppies out in her fenced yard unsupervised for fear of a hawk flying off with one of the pups. Our Sheltie is normal is most all respects and I know that Shelties like to talk. But she has such a fixation on things from above. She will even bark at airliners flying way overhead while my husband is holding her. You can't even hear the planes they are so far up, but she can see them. I just wonder if she was somehow traumatized as a puppy. We are thinking of trying the beans in a can, but she is so sensitive to noises I am not sure if that would make her bark more. I was thinking of keeping her on a leash when she is in the house so that I can stop her when she starts barking.

I had a Dalmation mix once that would bark at planes way up in the sky. It's odd.

This is what I would do: have her eyes checked and sign up for an agility class.

vicky