Play Biting

Question
We recently adopted a  one year old collie/terrier mix female. She seems to have a wonderful temperment and is very gentle when offered food and with the kids. However, when she gets very, VERY playful she play bites and nips. I don't believe this is anyway aggressive, but the nips can hurt. She also nips the back of your pants leg when she is very excited. Again, the nips can hurt if she catches the skin. How do I stop this behavior before it becomes more of a bite? We have 2 kids ages 14 and 8 and I don't want either of them nipped even at playtime.

Answer
This is not aggression and it is highly unlikely to evolve into aggression (actual "biting") unless you mishandle it and create a fear response. The dog is overexcited and is not able to contain its behavior.  Obviously, the best defense is a good offense: do not allow the dog to get into this agitated state.  If you see she is becoming a bit overexcited, put a lightweight leash on her.  This restraint is not only physical, but is experienced by any leash trained dog as psychological and emotional restraint.  Indoor leads (house tabs) can help a dog with low level seizure disorders to stop spinning and can center a dog with cognitive dysfunction.  Your dog's overexcitement is a form of cognitive dysfunction.  Lead her away calmly, do not make eye contact or touch her (as this will continue to stimulate her) and wait for her to visibly calm (could take two minutes or thirty.)  Meanwhile, learn about positive reinforcement training by going to karen Pryor's website or other experienced sources and teach this dog one SOLID behavior she can always succeed at (such as "sit" but use another word as most people ruin "obedience commands" by not teaching properly or following up properly.)  After 2 to 3 weeks of "training" (you're actually teaching the dog and giving her the option to perform), when she is overexcited (as you described), remove her for a short period by the indoor leash then ask for the behavior you can reward.  Once she has performed it and been rewarded, release her from the house tab.  Over time, she will learn to self calm, her overexcited behavior will extinguish and she will be more secure with your leadership.