it doesnt have to be 15 or 20 foot for a six hour dig mate , not all ground is softanoth, years ago all i worked was iner citys and have come up on sum right shit to get through to get down to the terriers ( concrete , old spring beds , wire , plastic, stone slabs are just afew obsticles to get through ) but thats the joys of inercitys and old tips !
when you get on long hour digs i think it does prove how good your dog is and also agree with wolfy that a dog shouldnt be breed from until its worthy , but again its all to do with what land you hunt , ive seen many a man work his terriers sor