1. A method of geofencing, comprising: a Kalman filter module to filter a plurality of past individual location fixes retrieved for a target device and produce a latest Kalman-filtered location of said target device; determining a predictive heading and velocity of said target device based on a plurality of Kalman-filtered locations; detecting a geofence boundary crossing by said target device based on said latest Kalman-filtered location of said target device together with said predictive heading and velocity; and dynamically determining time intervals between location fixes for said Kalman filter module using said predictive heading and velocity of said target device.