FYI I posted an ODK XForms-based solution for a geofence to the ODK Forum: https://forum.opendatakit.org/t/odk-geofence-v1/18656 . It can probably be adapted to your need (ie hardcoded geoshape fence instead of a user specified one).
It works fine under Enketo, but does require the latest version of Collect, as it depends on the new substring-after() XPath function in ODK. But I imagine this will get picked up in the next KoboCollect update.
