Rough Play

Question
I have a 17 month old, desexed female Great Dane. She has always enjoyed rough play including mouthing, running, tumbling etc. She is very submissive around adult dogs and plays well with most of them.She does on occasion choose a more submissive dog than her and nips their rump in an attempt to get them to play (which I know is regular dog play) but what is concerning is that if that dog does not want to play with her or becomes stressed she gets fixated with 'making' it play and she continues this and won't leave the dog alone  Recently she has also taken to fixating on playing with puppies # I imagine it is because they are more submissive than her too# and due to her size, their owners are not very happy when she puts their puppies entire head in her mouth!! The more I try to remove her from the situation, the more she fixates on that one puppy. I have taken a spray bottle down to the dog park with me to squirt her if she needs a reminder to slow down and this was successful until she got into 'fixation mode' when I just had to leave the dog park. I am not particularly worried about her hurting other dogs but she just won't leave them alone and even if I remove her for 5 minutes she will go straight back to that dog/puppy again. The owners often get annoyed as their dog can't play #not to mention the size of my dog freaks them out too!#I need guidance in how to manage her when more submissive dogs enter the dog park. Thanks so much for your help.

Answer
You need a "growl class" and you need to keep this dog out of the dog park until you've had professional evaluation and intervention.  If your dog hurts another dog, the cops will be called, animal control may be involved, you may be ticketed or worse (dog removed forcibly).  "Play" is a very specific behavior between/among dogs and is a function of social structure.  The description you offer ("fixation mode") seems to me to be a prey related behavior.  This dog is not presently a candidate for a dog park.  Spray bottles are NOT a method of intervention: this object is clearly part of "you", the dog's reaction to IT is directed toward YOU, the spray does NOT OCCUR in a manner that makes the dog connect its own behavior with the spray BUT it does confuse the dog and reduce her trust in you.  As a very large breed, the Great Dane SHOULD be gentle overall, not particularly boisterous; I think you need to do some serious work with this dog.  Positive reinforcement training in a professional training venue (with other dogs present, novice obedience class) is what I suggest.  Absolutely NO punishment, coercion or negative reinforcers should be used.  The dog needs to LEARN and that involves the use of reward as she voluntarily offers the behaviors you are teaching.  A group class will help her to learn to offer behaviors on cue, for reward, in the presence of all size of dog.  A "growl class" is especially designed for intervention in difficult dog to dog situations.  Ask your veterinarian if s/he can refer you to such a training venue.  If not, look online for positive reinforcement trainers with group classes.