Earthdog events are not close approximations of real work and are, in fact, a rather elaborate charade that obfuscates what is actually needed for a dog to be successful in the field.
The primary deficiency of earthdog events is that the tunnel pipes are enormous (9 inches by 9 inches), which means even the largest Kennel Club terrier can get down these artificial pipes with ease, leading some people to think even an over-weight Scottie can actually work in the field. Guess what? They can't!
While a go-to-ground tunnel has an interior space of 81 square inches, a real dirt pipe is likely to have a diameter of less than 35 square inches.
And while a go-to-ground tunnel has nice straight runs and smooth sides, a natural dirt den is likely to spiral, dog-leg back on itself, and present a tangle of root and rock.
And, of course, while a terrier in a go-to-ground tunnel is expected to bay a harmless caged rat for only a few minutes, a real working terrier will face real teeth attached to a body as large as its own for as anywhere from 15 minutes to several hours at a crack.
I am not against go-to-ground; quite the opposite. Anything done with a dog is a good thing, and more than a few people have entered the field after seeing the joy a dog experiences when the code explodes.
That said, I think no one should be able to get a "Master Earthdog" ribbon until the dog has actually entered real earth to real quarry -- and the owner had dug his or her own dog at least once.
In addition, the artificial den pipes for Master Earthdog, at least, need to be much tighter, with 18 inches of 6" round pipe at the front and another section of similar size and length in the middle.
If your dog can't get through a foot and a half of 6" pipe (a circumference of over 18"), it is too large to follow a fox to ground in a natural fox den.