Embodiments of the present invention include anchor assemblies and methods for using the same to immobilize a device within a body portal. In one embodiment, the anchor assembly is utilized to immobilize a catheter relative to a covered (e.g., skin-covered) burr hole formed in a skull. Anchor assemblies in accordance with embodiments of the present invention may include anchors located subdermally that may be unlocked from outside the body to release the device without a surgical procedure.