I have gotten a 2 year old rescue dog, he was basically in a cage for the first 2 years of his life. He now has a large yard to run in. He runs in a figure 8 in the back of the yard, and runs as fast as he can for hours. I have to bring him inside sometimes to get him to stop running. From all this running he is losing weight really fast. He eats in the morning and at night, but the weight keeps coming off. What can I do?:)