Just curious why you consider a Terrier a working breed?
e.g: border terriers were bred with a gait capable of following a horse so tht they could follow a horse on hunting trips, then they were trained to go down the hole and retrieve the prey, which could be a rabbit or a fox. There not a working breed in the sense of a border collie or a beagle but most were bred for a purpose, many dogs from working lines (like my harley) still have a very high prey dive and no fear of holes.
thats just an example of a terrier working but in the case of mach1girl i dont no how a pit bull terrier is a working breed but i no some terriers are lol