A method is provided, including providing an implant shaped to define a lumen and a flexible strip disposed at least in part within the lumen, and a plurality of recesses, the implant including a locking mechanism to which first and second ends of the strip are coupled such that the strip defines a closed loop which shortens when the first end is advanced through the locking mechanism in a first direction, and expands when the first end is advanced in a second opposite direction; advancing the first end in first and second opposing directions with respect to the second end; maintaining a recess-engaging portion in a position in which the recess-engaging portion is not disposed in any of the recesses during the advancing; and restricting the advancing by facilitating active positioning of the recess-engaging portion in one of the recesses. Other embodiments are also described.