My girlfriend and I adopted a 6 yo lab mix about 6 months ago. He is generally a very sweet and affectionate dog, however last week he was laying on the bed next to me, and when she leaned over him, he growled and curled up his lip slightly. She leaned over again, and he snapped at her (did not bite, but it scared her). He is around both of us all the time, but I've noticed he follows me around much more often, and even if he is sitting with her he often stares at me. He is typically fine with her other than this one incident, he will lick her face and generally be affectionate. It seems like it's only when I am around that he becomes possessive. I want her to feel safe around him, he is technically her dog afterall. But I do most of the walking, and am the one to take him outside morning and evening. I suggested to her that she start taking him on long walks to bond, since he doesn't seem to view her as the "alpha". Any other suggestions?