This invention relates to an elongate medical device, with a distal end to be advanced into the body of a patient and then withdrawn from the body and an elongate shaft connecting the distal end with a proximal end that remains outside the body, the shaft extending in use through a hole in the skin of the body characterized by a slider, captivated on a portion of the length of the shaft, which is capable of lining the said hole, as the shaft is advanced and withdrawn relative to said hole and the slider in the hole, said slider having a maximum outer diameter that is substantially the same as or Jess than a maximum outer diameter of the distal end.