Techniques are provided to dynamically generate and render an object bounding fence in a mixed-reality scene. Initially, a sparse spatial mapping is accessed. The sparse spatial mapping beneficially includes perimeter edge data describing an object's edge perimeters. A gravity vector is also generated. Based on the perimeter edge data and the gravity vector, two-dimensional (2D) boundaries of the object are determined and a bounding fence mesh of the environment is generated. A virtual object is then rendered, where the virtual object is representative of at least a portion of the bounding fence mesh and visually illustrates a bounding fence around the object.