Dogs may growl, lunge, or bite to protect items they consider valuable, such as food and toys. The behavior, known as resource guarding, is an essential survival instinct in feral dogs, which helps them thrive on limited resources in the wild. However, for domesticated dogs, it is a dangerous problem.
Experienced dog parents know not to disturb a dog when eating or playing with their favorite toy because there's no telling how they might respond. Some dogs don't mind being interrupted during mealtime or playtime, while some mind.
Resource guarding is not specific to any dog breed and can easily be identified by watching certain body language dogs exhibit. When dogs guard an item, they may stiffen their body over it, give a hard stare, growl, or bare teeth.
The best way to prevent resource guarding in dogs is to start training them as early as possible. In a situation involving an adult dog with this tendency, Nicole Costanza, the founder of Momma's Dog Training in New Jersey, advises that you slowly desensitize them to your presence around high-value items.
Some dogs suddenly become protective of their food, toys, and personal space in adulthood. Such changes in behavior could signify an underlying medical condition. It would be best to consult your veterinarian or a dog behaviorist and have your dog checked.