This is pretty awesome -- there's a group called the People and Animal Cardio Klub (PACK) which works with the Washington Humane Society: you join the club and then run with the dogs, so they get some needed exercise, and you do too!
You pay just $10 to join, fill out the form, and after some orientation and an interview, you can help out.
It sounds like a great idea, and helps a great organization find homes for dogs. Rock Creek Park seems like a great spot for it too.
Here's more from their website:
H/T to Active Life DC for the heads-up
Photos from Pack's Facebook page.