Leonbergers are supposed to be noble, gentle and sweet - and many are. There is no guarantee though, only good breeding practices with an emphasis on an outstanding temperament significantly increases the chances that your cute puppy will grow up to become a gentle adult.
Behavior is not only the responsibility of the breeder but also of the owner. Leos are large dogs and are frightening to many people simply by virtue of their size. Fear and aggression in a stranger can activate a dog's protective instincts. Large dogs can also do a great deal of damage just by jumping up on someone in a burst of enthusiasm.
In some Leonbergers, there is a fair amount of play drive, as in most dogs. Running children will be seen as an invitation to chase - with a 120 pound dog that might be problematic. When you invite a Leonberger to share your life, you bring to that contract the responsibility to make sure that both you and your dog receive excellent obedience training.
To become excellent family and watchdogs, Leonbergers must be well socialized as young puppies and extremely well-trained and under the control of their people at all times. It is difficult to train a dog that has been improperly socialized. The fear of parvo has led some owners to make the tragic mistake of keeping their puppies isolated until they have completed their vaccination series; they risk ending up with a fearful, timid dog that may become aggressive as an adult.
Owners must strike a balance: Puppies, especially from birth through four months, must be exposed to a variety of people and experiences. There are many parvo-safe activities and places to take dogs, and new owners have to take the time to expose their new pups to as many of these as possible. This is especially true for one's second and third Leo; it is too easy to keep the new pup in the company of the older dogs, depriving him of the opportunity to develop self-confidence.
Leos are known for their stability. As a general rule, they are consistently even-tempered and generally pleasing to be around even in noisy and chaotic situations that would be highly stressful for some other breeds.
A typical and impressive sight at dog shows and gatherings is a large "pride" of Leonbergers peacefully and contentedly sitting and lying together in close quarters. However, on closer observation one will find that males in the midst of "hormone storms" are carefully separated and have been placed at opposite ends of the group.
