First off, I am so sorry you're having issues with your shunt. I'll be keeping my fingers crossed that the medicos can come up with a fix so you can continue your active life. Generally speaking, life with a dog is better for one's health than life without. I genuinely understand your concerns -- DH and I waited 25 years to get a dog because our military life (we were both Air Force) might mean deploying at the same time. But with a fenced in yard, coupled with your own need to walk to some degree for your own health and sanity, I'd say you'll do well. Shelties are very adaptable!