My 2-year-old papillon has recently started growling in what seems to me to be a protective manner. He mostly does this when I or someone close to me is lying down, particularly in bed. If someone approaches, he fairly frequently gets upset and growls. He's never lunged or tried to bite anyone, or even moved towards them, but I'm concerned - should I try to curb this behavior before it grows into something bigger, or let it peter out on its own? He also occasionally growls when he feels threatened, such as if a stranger approaches him very loudly when he is in his carrier. I'm less concerned about this second behavior, especially as it's quite rare.
I think the "bed growling" stems from his losing his previous owner - before she passed away, she slipped into a coma while in bed and the paramedics had to come and take her away. He was there the whole time, and started growling like mad when the EMTs came in, and poor little fella, that's the last time he saw her.
With that in mind I think his behavior is understandable, but again, I'm concerned that a growl might turn into a nip or something worse and I don't want to encourage him.
So far I've touched his back and said, "Shh, it's okay" and then an emphatic "No!" if he did it again, and then tried to demonstrate that the person approaching was a friend. He calms down quickly, but still... Any advice would be much appreciated!