My best ferreting dog I had was a whippet x springer spaniel.
100% at marking, never touched the nets, but caught those that slipped the net.
What set her apart though was that she would mark layed up ferrets and 'paw' the ground directly over them, she was rarely wrong.
Sadly that was 25 + years ago and it's like a lot of things you only realise what you have got until they are gone.