A: Same-sex aggression and aggression towards other breeds of dogs is well documented with this breed. It is strongly recommended that no more than two Jack Russells (of opposite sex only) ever be permitted to stay together unattended.

• Most behavioral problems are due to a lack of companionship, discipline, activity and exercise.
• For a Jack Russell that is very aggressive with other dogs, a technique is to squirt the terrier in the face with water whenever he growled at other dogs. No scolding or other action is required in this instance - just a surprise squirt.
• A Jack Russell Terrier that bites can be a big problem. You must stop this behavior before it becomes dangerous.
• Don't allow your Jack Russell to win any games of aggression. The outcome could certainly send the wrong message to him.
• Exercise, exercise, exercise! A tired dog seldom want to pick a fight.
• Never put your hands between two fighting terriers
• Jack Russells require firm, consistent discipline. They are extremely intelligent, continue to test their limits throughout their life.
• Jack Russells can become very possessive of their owner or a favorite member of the family or of what they consider to be their personal property if allowed to do so to the point of showing aggressive protective behavior that must be controlled from an early age.
• Jack Russells can be very destructive if left unattended and unemployed! Most behavioral problems are due to a lack of companionship, discipline, activity and exercise. If you've only seen perfect, well-behaved JR's, they are ones that were lucky enough to be exercised, well socialized, and trained.