Years ago ,trust me nobody put a single dog in places you would today .Earths were trenched to find a dog in a deepish place and sometimes ruined.Its very nice to fantasise and reminise about the good old days but lets face it, today with the collars we have now ,one dog ,one hole is the hoped for result however deep .Yes the collar does allow the use of mute dogs but all mute dogs ive come across are mute for a reason ,a mouthful of charlie.