Meaning of phrases

Iwould like to find the meaning of the following phrases:
to go to thedogs
to put on the dog
to throw to the dogs
to teach an old dog new tricks

Just another spin on. "to go to the dogs" and. "to throw to the dogs" More on their origin than on their meaning in modern day parlance. In primitve societies long ago and even today, when humans took on the hunter gatherer roles, packs of domesticated wild dogs were always a part of the community as they served many useful purposes. However when it came time to feeding, the dogs were certainly last on the list of food recipients, or warmth or shelter for that matter. Hence to go to the dogs refers to the condition of anything that is no longer useful to the general population." HJR