hello all, I have a 5 year old dog who's never really shown any signs of aggression before until recently. A few weeks back he would kind of growl at my Girlfriend whenever she would come towards his general area faster than usual. this only happened a few times until the other day she was helping me take off my boot and he actually gave her a small nip. Today he grabbed one of her socks and when she tried to get it back, he growled at her and barked and displayed some very standoff-ish behavior. at this point i gave him a slight smack on the rump. all of this happened after she got done petting him for like 20 mins. What am i I doing wrong? any ideas as to what could be going on? What can i do to address this issue. I would like to think he would never actually try to bite her but at this point it looks like a possibility. Thanks!