Dealing with an aging dog

Rex will be 12 this month. His health is increasingly becoming an issue with him. I'm know I'm entering into the area of what is best for him. I keep telling myslef that this is about him not me.

His main health concern is his hips. They have become very weak over the last years. He frequently falls back on his butt and is unable to get up. The look on his face when this happens kills me. He just looks so sad and helpless. "It sucks getting old daddy"

I will write a detailed report on his last days on this earth with focus on what is best for him.