alot of people will have diffrent prefrances but this is mine firstly for the area i dig in i like a dog with a bit of size about them built for the job as some would say a terrier of around 14 -16 inch and around the 20 lbs mark suits me dog has to have agood nose be willing to dig on or push on through tight areas preferebly i liek a baying/ mixing dog one thats up in thier face letting their presence be known and one that has staying power to see the job through and one that ups the tempo when the going is getting tough .... but remember lads the best dogs have bad days if your out doing en