Electronic geofencing is proposed as a means to manage small unmanned aircraft systems in distinct airspace boundaries. A geofence is defined by a minimum and maximum altitude and a polygonal horizontal boundary. To ensure geofence boundaries are respected, geofence enforcement software activates before a boundary violation. This paper proposes an algorithm to scale geofence boundaries such that new layered warning and override boundaries meet minimum distance constraints from the original no-fly boundary. Each minimum buffer distance is specified as a function of vehicle performance constraints and environmental conditions such as minimum turning radius and persistent wind. Supplemental procedures increase the usable flight volume given irregular polygon shapes. Monte Carlo simulation studies statistically validate our layering approach and identify polygon geometries difficult to layer.