Abstract: A device for alternately restraining movement of each end of a powered extensible and retractable link having first and second sections. The device is contained within a housing which can be inserted into a toolbar and attached to row marker assemblies to alternately lift and lower each row marker. Included as part of the device is a housing having channels therein for guiding linear movement of the link sections, a detent lever for alternately restraining movement of each link section and an actuating mechanism which causes the detent lever to alternately engage and release each link section.