well i'm no "terrier man" but i've done a fair bit of digging over the years...and i've had and seen some decent russells....that stay until dug..
maybe they are like hens teeth but could'nt that be said about all terriers.....
the one i have now is only a young dog but he's had over 30 digs....and never once failed....not all hard digs but he's had a few awkward ones.....and theres lads on here that can verify this.....
Patch....my castrated Russell .