A target tissue localization assembly includes a radially expandable tissue anchor connected to the distal ends of an anchor assembly and an elongated anchor actuator element. A lock, engageable between the actuator element and the placement element, may be used to prevent collapse of the anchor from its radially expanded state. A sheath may be slidably mounted over the anchor assembly. The sheath and the anchor assembly may be configured to permit the sheath to move in a proximal direction, relative to the anchor assembly, past a chosen location while preventing the sheath from moving past the chosen location in a distal direction.