[color=darkblue]Thanks everybody for the suggestions [/color]:)
We've taken her to the vet. The vet didn't find anything wrong with her except that she needs an attitude adjustment. Her behavior should've been stopped the first time it happened. We've been letting Trista get away with too many things for far too long. I can't take her to obedience classes because she panics and stresses out whenever she's around strange people and other dogs. Her personality is not typical of a sheltie, she's very independent, stubborn and territoral. The vet said I could train her myself by being very firm, patient and decisive with what I want her to do. Because of terrier-like temperament I can't train her like the average sheltie,she'll have to work for my attention/rewards and give a harsh, quick correction with a collar & leash if she doesn't submit. I also have to start training her like a Rottie or Bullmastiff instead of viewing her as a sensitive sheltie or spaniel.
[color=indigo]Its ironically funny because my other dog Ryo, an Akita, a breed known for aggression issues, has the bubbly, easygoing personality of a labrador and my supposably gentle, "innocent" sheltie has the complex, apathethic, obstinate temperament of a Chow Chow. [/color]:niedowiarek: