A system for making sure that two wireless devices (a perimeter-anchoring device and a constrained device) are not separated too far apart by having a dynamic perimeter that follows the perimeter-anchoring device as it moves. In some embodiments, the size and/or shape of the perimeter is controlled by machine logic based rules, based at least in part, upon a set of environmental factor(s). Some possible environmental factors include: line of sight, pollution, noise level, presence of stranger(s), streets, traffic, body(ies) of water, contamination, allergen, or blocking obstruction(s).