I can get her to dig on command by just pointing to the mole line in the grass, but if my wife catches me doing that I get yelled at by her for encouraging it.
That's how it all got started. I had a shovel and the dog was following me to the garden (she was 6mth Ger. Short Hair puppy) I saw the mole trail and dug it up a little and showed her the hole. She got a smell and has been digging and killing moles for nine years. Little did I know what it was going to turn into, if I could get her to stop I would. I think the first year she killed 50+ moles. She can even find them the early part of winter before it freezes the ground with snow cover. She walks slowly and listens for them, when she hears them she's starts digging. The population has been curbed since then, now it's only 10-20 a year, but I think she's upset the natural balance. I've got big patches of dead grass from grubs, I've got grubs like you wouldn't believe.