Dog aggression (opinions on what working lines are known for it ?) - Page 4

I have a brother and sister linebred Yoschy with Pike inclusion . Both are dog aggressive, I think.  I do occassionally let them run together.  Lots of HARD PLAY!  I figure this is trying to assert their domnancy.  Eventually female gets tired and no more play.  But, put another dog in the picture, which happened the other day.  Male hop the 6ft.fence and nearly killed the next door dobie. Medical bills, dog and owner next door.  On the field, and on the long down, you can see they are ready to pounce.  Not sure I can get them titled for this.  Drive galore! Everything you want in a GSD, well.....could use a bit more civil.  I think at this point, mainly sports.  Will breed the female, when it's time, to a bit harder, civil dog, if all goes well in the physical and titling requirements.  Question is whether DA is a learned behaviour or a genetic trait. 

tenmom sorry to hear about your male jumping the fence and hope all works out ok, I think DA can be both learned and a born with trait,,, to me the worse cases i,ve seen over time seem to be born with it, I dont know anyone that would try to foster that behavoir at least not on purpose anyway,but you hear of such cases in the news now and then, I had a female once that i was too fearful of trying to title her she was the type if she saw one other female that even looked at her wrong she would go nuts and in her head it was game on to me its such a shame when the drives are so nice other than the desire to fight that some have.