I have a South African Mastiff. He has always been very sweet and lovable. However, I was unable to keep him so my mom offered to take him. He is great with her and her other dogs. No aggression towards any of them. However, he does show a lot towards my moms husband. But he never did before. We have no idea what this is caused be he is not an animal lover and wants to see all of them go but especially the mastiff. Any ideas?