In general, the invention provides improved sheaths for enhanced control over the relative position of the sheath or inserted catheter relative to a biological tissue. The invention also provides improved sheaths for controlling the longitudinal and axial movement of inserted catheters relative to the sheath. The sheaths include an active anchor at the distal end capable of reversibly adhering the sheath to a tissue. Exemplary active anchors include a reversibly inflatable balloon, a deflectable tip, a suction cup, a screw, and a barb.
