If you want to learn more about training and controlling your Jack Russell, my ebook is bound to save you hours of training trial and error and relieve a lot of stress from the process: The Jack Russell Lover's Ultimate Guide to Training comes complete with a full chapter on mix breeds.
We have a new Jack Russell female (now 7 months) who we have introduced to our 11 year old (both Jack Russell, both female) who were getting along fine the last 5 months. We introduced a new male kitten two weeks ago and have been very proactive in the introductions which have been working really well until tonight. I think we may have done something wrong separating the introductions (thoughts of 2 Jack Russells against a kitten). The younger who is probably vying for dominance has been vicious over a joint meeting of the kitten to the point of attacking the elder female dog and drawing blood and will not back off even after they have been separated. We have had to isolate their sleeping arrangements tonight (as they always sleep together), want to nip this in the bud asap before it esculates. Any help appreciated.