[haypoint]

There was a dog cross like that in an animal shelter that I inspected. Had been adopted a few times, but always brought back. Two high energy breeds crossed with far different instincts, created a nightmare. With the hundred different breeds of dogs, I cannot think of a worse cross.
Terriers are in ground hunters, hence tera ferma, earth, in their name. Healers have an intense instinct to herd cattle, and sometimes anything that moves, by heal nipping.
Either breed should only be owned by someone that can keep the dog busy, a well structured job. For a terrier that would be lots of rodents and plenty of digging area. For a healer that would be a good size herd of cattle that need moved frequently.

 

[haypoint]

Haypoint...I agree to a point. We have an ACD/GSD mix

IMHO, a German Shepard is a dog with instincts to react on human voice commands, as is a cattle dog, while a Jack Russell is a high energy of instinct motivated digging, biting, jumping fireball.
That you obtained a middle aged dog and you apparently had the time to satisfy that energy was a big help. No one should ever own a working dog breed that cannot provide a constructive outlet for that energy. No one should ever own a Jack Russell unless they have a constructive outlet for their digging/hunting instincts. I cannot imagine a home/family/situation/owner that could satisfy the mixed up mess of Cattle Dog/Jack Russell puppy. But that is just my opinion.