if the dog marks the earth from a distance . you enter it . the same dog on a different day may need to run through to find. yes I would say its about scenting conditions. but that don't change the fact that some dogs shine above others in the nose department. if you are out with a few terriers you tend to rely more on certain dogs for finding than others. experience comes into it but generally speaking a dog with a good nose shows this very early. as does a poor one when in company. you also need a decent owner to read the dog. as for hard terriers that's down to how you define this. ive seen