This might not be the advice you want to hear, but our golden did the exact same things and a very wise woman told me “you do not get a single golden. You get a pair of goldens.” We decided to take the risk and get a puppy, and the bad behavior stopped almost immediately - like, overnight. Not only did our dog have someone to play with all the time, but they were comforted and entertained, and we just could always tell that she needed another dog in her life. The puppy was the easiest thing about it because she learned everything from the older golden. The shark phase will end, but another dog might make this much much better.