Petometer: This very cool app from Purina maps your dog walks via GPS (be sure your location services are turned on, or it won’t work). Routes are marked with little pawprints, and time and distance are recorded for each. Set up as many walks as you wish and keep them archived for future reference. Petometer even has recommended exercises—all without any ads. Free.
Runner-up: MapMyDOGWALK, works fine, although it’s not as elegant as Petometer and has lots of ads. Free.