Systems and methods are disclosed for dynamic band boundaries in data storage devices, particularly devices employing shingled magnetic recording. Band boundaries may be modified to include spare sectors from guard areas between bands to achieve field defect-slipping. Band boundaries can also be shifted to migrate spare sectors from one guard area to another in order to dynamically distribute spare sectors. In one embodiment, an apparatus may comprise a data storage medium and a controller. The data storage medium may have a first and second sequence of circumferentially adjacent data sectors, and a first guard area disposed between the first and second sequence such that no sector of the first sequence is directly adjacent to a sector of the second sequence. The controller may be configured to restructure the first sequence to include a sector from the first guard area to produce a shifted first sequence.