Summarize this article in one sentence.
Running pens are similar to starting pens, only larger. Your puppy can track farther afield here, and continue to use its nose rather than its eyes to locate the rabbits.  Running pens can vary widely in size, from 5 acres all the way up to 100 acres or more. To save time and money, join a local gundog field trial club. Most clubs will have both starter and running pens that you can use, as well as professional dog trainers who can help with puppies or dogs that are proving more difficult to train. Keep close to your puppy most of the time to build a strong team relationship. This should occur when your pup can independently track a rabbit in the pen for around 10-20 minutes.  A "brace," or two-dog pack, is often created by pairing your puppy with an older dog. Your pup will learn more advanced tracking skills from the older dog, in particular how to behave during a "check," or temporary loss of a rabbit's trail. Aim to run your young dog with a trained, but slower, female. If you only have one puppy (or puppies), you will have to run it with a friend or neighbour's dogs, or visit the local gundog club. Introduce your dog to gunfire training early on, in order to prepare it for the loud sounds of a hunt.  Gradually train your dog to tolerate gunfire. Incorporate low-level, distant gunfire into daily activities, only moving closer as your dog becomes accustomed to the sound. Do not suddenly fire a gun near your dog if it has never heard the sound before.

Summary:
Move your puppy to a running pen. Let your puppy run with older, trained dogs. Prepare your dog for gunfire.