[Checkers]

I don't know if any of you will be able to help me here or not but I will describe the events as best as I can and see what we can all come up with. First to re-familiarize you with our set-up. I have Cheyenne, a 10 year old shep mix (approx 50lbs or 22.6 kg) and Checkers the PWC (approx 30lbs or 13.6kg). To give you a little background... Cheyenne is the strong silent type. She has shared her home with several other dogs through the years (mostly rescues) and typically I can get her to behave around most any dog after about 5 minutes of introductions. However, some of the dogs we have kept she will still try to dominate. I'm not sure if that is the right assessment... but if the other dog tries to walk by her (even if the two of them were playing happily just 30 minutes prior) she will curl her lips and growl... and it isn't a joke. She has done this with Checkers before... but the last two times he hasn't backed down at all and they have ended up in a full-out fight. This happened tonight. I was playing fetch with Checkers... the ball went past Cheyenne and when he went to retrieve it (totally not even paying attention to her because he was going for his ball) she growled and then when that didn't work and he bounded past her she went after him. Luckily my husband and I were both right there... I grabbed Cheyenne rather easily (she isn't too hard to control once you have her by the scruff) and my husband had to pull Checkers off of her. They were both completely beyond hearing or seeing us at that point. We scolded both of them (verbally only) and put them both in a "time out" (just to get them away from each other while things cooled off.. not because I think dogs know what time outs are). After about 15 minutes we let them both back out and I stood between them and made sure they both understood they had to submit to me before they were allowed back in the main room with us. I did this just by my own body posture, not through any physical touch. When they both were laying down comfortably and calmly (a matter of a few seconds) we let them back in with the family. For the rest of the evening I kept a very close eye on each of them to make sure they weren't showing dominate type posturing around the other one.

Now for the questions.... why does she seemingly turn aggressive at him just for running by like that? What can I do to prevent that from happening again? These two play together almost every day, eat close to each other with no problems at all.... have even been caught sharing a bowl! Neither has ever demonstrated food or toy aggression with a human. This has now happened twice and while I have broken up more than my fair share of dog fights (tends to happen when you get a lot of strays dropped at your house) I don't want to do it again... especially with my now 5 month old son in the house! Is this something I should try and consult a local behaviorist about or am I just missing a clue. Any thoughts? Thanks in advance... and don't worry, I can take a beating LOL!

-Cheryl