An instrument for deploying a marker at a site within a patient may include an elongate cannula, an elongate pusher, and a marker disposed within the cannula. The cannula may have a tip at its distal end and a transverse opening. The pusher may be disposed within the cannula, and may be moved longitudinally within the cannula. The pusher may have a ramped distal end. The marker may be configured to exit the transverse opening upon urging by the ramped distal end of the pusher. In some versions, the tip of the cannula has a flat proximal face, and the marker has a recessed region that is configured to buckle in response to longitudinal compression, such that the marker will pop out of the cannula upon buckling. In other versions, the cannula has an external sheath, an open and curved distal end, or a leaf spring.