"I doubt he'd need to, a 180 GSD is morbidly obese ... wouldn't be able to catch the jack russell in that case."
Haha, yes, very morbidly obese. Ever notice those Czech bloodline GSD that the police and military use for K-9s, those are full grown at 70-75lbs (the perfect weight and size for the breed, American bloodline GSD are too big, heavy and have way too many health problems).
Document with the police, video record any further incidents, document dates, times, witnesses.
Get a bottle of wolf urine, spread it along the border or the yard by the street or sidewalk, all dogs (small mammals, bears, coyotes, cats, foxes, etc) are seriously afraid of the smell of wolf urine.