Yorkie with ADHD!

Today I took a walk through the snow with my friend and her hyper-active yorkie. He was madly excited, kept running ahead of us as far as the lead (and the hand holding it) allowed, as he always does, and enjoyed the fresh snow. His owner told me that if she let him off the lead, he'd run, and run and run till exhaustion stopped him. Then he'd look back for her and be surprised not to see her. She tried that once or twice in a secure place.