The first step is to set a Geofence pin on an address field (usually the Tow Yard). Go to the Tow Yard form from the setup page and click on Fields.
Edit the Tow Yard Address and select the Geofence Tab. Select how often you want the Geofence to be active and the geofence radius. 100 meters is good radius, especially if the user's iphone GPS drifts.
Verifying Time card can be turned on through the user profile under mobile app options. To learn more about User Profiles see this article. Company Users
Employees that have Geofence enabled will only be able to clock in on their phones within the determined radius of the pin. This is EXTREMELY accurate, and even if their phone GPS drifts and they are .00001 off that will still not be able to log in.