While Dr. Ishigaki was visiting he showed us a very cool method for freeing two segments that are stuck on a tenkara rod (or any telescopic rod). It's very simple, and effective, particularly if you have pieces that are stuck very tight or one of the thinner segments is stuck. I still recommend the tapping method in the field or for most cases as that will normally take care of most cases. However, the rubber band should be used  if you have a hard time freeing the pieces: