I have combined presence set that if EITHER WiFi or Geolocation arrives, then I am home. On the other hand BOTH have to be gone for me to be not present.
It works fine as long as you have a phone that doesn't shut off both signals, or as long as your phone isn't off or something.
You can also set a time-out so your phone toggling or a blip somewhere doesn't trigger presence change.
Edit: this is the particular app I am using. There are other similar ones out there also. [RELEASE] Combined Presence