A young sheltie ties to convince a much larger sheep that it is serious and up to the task.
When a working sheep dog moves sheep, he is said to be exerting "pressure" on the sheep by using body language, movement and voice.
If the dog puts too much pressure on the sheep, they may scatter in several groups or bolt off stampeding in the wrong direction. If the dog is too aggressive or too timid, a protective ram may decide it can bluff the dog into submission or that it must charge the dog in order to protect the ewes. Under either scenario, the dog can end up being chased by the sheep.
Herding is difficult because every flock is different, and so too is every pasture. A working collie cannot afford to make too many mistakes, and that is especially true in a timed herding trial.
If the dog is too amped up, it may press the sheep too hard and they will bolt and remain spooky for the rest of the run. If the dog does not put enough pressure on the sheep, however, they will be slow to lift and valuable seconds will be lost on the clock.
While things are a bit different in the world of working terriers, the concept of pressure is the same, and the same kind of see-saw is at work, only it is all done underground.
If a terrier does not put enough pressure on a groundhog or badger, it may dig away and soon be lost to both dog and digger.
Conversely, if a terrier puts too much pressure on a groundhog, fox, raccoon or badger, the animal may decide it has no other option but to stand and fight. If that occurs, the dog may be injured.
Intelligence and balance are treasured and valued in working collies. As Patricia B. McConnell notes in her very good book, The Other End of the Leash:
"A good, steady dog with an innate sense of pressure is worth his weight in gold, because he can move sheep or cattle without causing a fight or a stampede, smoothly moving the herd where you want them. The brilliant ones make it look so easy, you wouldn't know what all the fuss was about, until you watch a dog with no finesse, who moves in too fast, and panics the flock."
The same can be said about a working terrier. When a really experienced and well-balanced dog goes to ground, they do not rush in full of fire and belligerence, but creep in listening. They are not trying to move anything yet -- they are simply trying to locate, and they are trying to get a sense of how much pressure will be required to move whatever is in the hole.
When the dog does locate and opens up to a bay, he will be using his voice -- and probably his voice alone -- to move the quarry to a bolt or a stop-end of the den pipe. While a young and inexperienced dog may rush in with grabbing teeth (and get the muzzle bites to prove it), an older and more useful dog will know the easier way to get the job done.
The quarry in the hole is not the only thing under pressure, of course -- the dog is too. The pressure felt by the terrier is directly proportional to: 1) the amount of experience it has had underground; 2) the size of the hole it is working, and; 3) the mood of the animal it is facing.
I think this is the proper ranking of the main pressure-builders within a working terrier. An experienced dog is comfortable underground and knows enough tricks and ways of working that it is pretty confident that it can get the job done no matter what is found down there. An inexperienced dog, however, is not battling the quarry so much as its own fears.
Whether the dog is experienced or not, frustration rises and falls in direct proportion to the size of the hole. Even a confident and experienced dog feels pressure and frustration in a very tight hole where it cannot move forward or backward without substantial struggle.
The quarry itself can exert pressure on a dog, of course. Both a raccoon and a possum can make enough noise that they can spook both dog and digger alike. Groundhog and fox, on the other hand, are less likely to voice their objections than demonstrate them with slashing teeth.
All of this take place in the pitch black, of course. While a sheep dog can receive visual cues from the sheep, the terrier must rely solely on sound and scent. And while too much pressure on the sheep may result in the flock moving too fast or breaking in two, too much pressure by the terrier may result in a rip to the muzzle that will take weeks to heal.
At the end of a dig, just as you are breaking into the pipe, is when things often go bad when you are working terriers. Emboldened by the presence of light and reinforcements, a terrier that has used his voice alone up to this point, may decided it can now go in and grab.
An experienced terrier will try to grab his quarry by the cheek or ear, since a groundhog, fox, or raccoon gripped by the side of its head cannot easily move to bite back. Not every dog is smart enough, or lucky enough, to get such a good hold, however, which is why a smart terrierman will generally step in and pull his dog as soon as he can in order to save his terrier unnecessary injury.
Bottom line: As it gains experience, a working dog learns to relax a little more and begins to develop a bag of tricks and techniques it can employ to tackle different situations. In both herding dogs and working terriers, an experienced dog learns to stay attuned to the pressure building up on the other side of the field or pipe. There is a fine line between too much pressure and too little, and the very best dogs walk this shifting line with the grace and skill of a ballet dancer.