I agree with the half cross theory, but also I think in fairness you should be talking about hard driven dogs only,as these types test durability.Any cur can avoid knocks.A dog that does what he can to catch whats in front of him regardless is the one that needs to be durable. Ive seen some very hardy half cross Collie/greys and ive seen others (well known breeder)that tried to catch a rabbit on plough by running around the headland after it. The owner tried to laugh it off and say hes clever but I could feel his shame. The Greyhound needs to be reduced to at least half whatever you cross it w