The Parson Russell Terrier is a playful, loyal breed that has a fearless nature not expected from a dog this size. They are smart, but willfully so, making training a bit of a challenge. They can also be aggressive toward other dogs, and because of their hunting background, should not be left alone with smaller pets. In order to properly train a PRT, they should be trained with a firm, confident demeanor -- they need to know that you are the boss. They also require ample exercise and can get destructive if not given a healthy outlet. However, with enough exercise and patience, this breed can be a devoted member of the family. .