A stud dog is only as good as what he can produce. If you put a good dog to a variety of good bitches and he doesnt throw anything worthwhile then he cant be called a good stud dog or prepotent I think the correct word? It doesnt matter how good a dog is, if he cant reproduce himself well then theres no point using him over your bitch. Its best to always try to use a dog thats not only proven in his field ie coursing, digging or whatever, but also a dog that has consistently sired good pups with the same sort of qualities he himself possesses.