Along with many other breeds, many dogs that retrieve guard their resources both from each other and in some cases their owner as well.
What is it and how does it manifest itself.
A dog who resource guards. It often manifests itself as a dog growling or otherwise being aggressive. That aggression can be directed either at you, another family member or a pet.
How to address this.
Prevention, as with all things, is better than a cure. Theres lots of things not to do – avoid them and worsening the problem. More than anything never punish a dog for exhibiting guarding behaviour., any punishment will be seen as rewarding behaviour.
Train in such away as to teach your dog that not everything belongs to them and they can only take things with your permission. If athts not working you may need to consult a trainer of behaviourist to help.