My Jack Russell

you could still change his name..
this is probably the source of most of his problems..
when you say "Here Bo". to Bo, it sounds like "HERE, NO"
it is a huge contradiction..

i would change it...

a good friend of mine adopted a dog named Teddy from a shelter, he was 5 years old and his name has always been Teedy. She changed his name to kaedyn.. he listens to it fine..

anyways.. i think that is your best option next to phoning around to different obedience trainers....
good luck