[OSUcowgirl]

We have a two-year old male, black lab. If we are present, the dog will usually cower behind us and avoid interacting with strangers and guests. However, if we are not right there, he is becoming increasingly aggressive.

The other day he snarled and threatened to bite someone who stopped by. Today, my father-in-law stopped by and the dog bit him after he got out of his car. My father-in-law is a stranger to the dog, but had not approached the dog or made any attempt to interact with him. The lab simply ran toward him as if to greet him, but instead went around behind him, snarled and bit him very quickly with little warning.

How do I correct this behavior in an older dog, especially when he exhibits the behavior when I'm not around, but acts fine if I am present?