Walk For a Dog by Wooftrax is a FREE app. It uses GPS to track you when you are out walking your dog. You are able to select a shelter of your choice to walk for and every mile you walk earns your shelter a donation. It's a really simple way to donate to a shelter you love and a great way to encourage you to get out and walk with your dog. You don't even need a dog! You can just go for a walk!
This is an awesome app and it works on both android and iPhone.