i might be of a different opinion here, are we saying that the only dogs good to ground are stayers? have you ever worked a "flyer"? they find,harass and when it gets hot they move.find again often from a different approach.i have had a bitch and her bitch pup who both worked like this and no fox held it out long with them.they only made contact at the arse end(neither were ever marked and some foxes bolted with the brush stripped).both were tested in trials and did well.
digging is not the only way to bag the fox.what of the earths we cannot dig?
dogs like this will work seven times a we