Some of this is not a training problem, and treating it like one wastes time your dog may not have. If they are distressed when you leave, if they growl or guard their food, their toys or you, if they are frightened on the lead, or if anything about them changes suddenly at any age, contact your vet the same day. A tip from a website, ours included, is not the answer. If it cannot wait, contact your nearest emergency vet now.
With a Chow Chow, watch their eyes and their mood. Squinting or rubbing their face can be their eyelids rolling in. A Chow who becomes grumpier about being touched may be in pain from their hips or elbows, not getting more aloof. Slower, heavier and thinner in the coat can be their thyroid. In a Chow past ten, restlessness at night can be the start of cognitive decline (a slow loss of memory and routine). Bloat (GDV, a twisted stomach) can happen in any dog, though it is most common in large, deep-chested breeds. A swollen, tight belly, retching with nothing coming up, sudden restlessness or drooling is an emergency: contact your vet now. It is easy to put the rest down to character, and that can cost months.
He'll keep vetting your guests slowly. If he starts to growl at one, tell your vet.