A good ferreting dog is a god send saves you time and does a lot of work for you.
As Robert Michem said it's not just about catching bolters it's also what they are trying to tell you, sometimes the lads with the dog don't see the signals, some dogs mark subtle some dig at the hole and make it obvious. I think any dog for ferreting should mark, and be respectful of nets and ferrets, the bonus' is dogs that really let you know whats going on underground once the ferrets are in. I love watching the dogs mooch and ferret thats when you see a dog working properly in my opinion, I love lamping but