serious anus problem

i have a leopard gecko and where his anus is it looks to be a scab that stretches from one thigh to the other.  it es real hard and does not seem to be sensative to him at all when i touch it.  

[Aleda M Cheng, D.V.M., C.V.A]

It sounds as if your gecko has had a rectal prolapse that has scabbed over.  Gecko's can get these these from straining excessively from a variety of causes including intestinal parasites and from dietary causes.  In females it can also be caused by straining to pass eggs.

This can be a serious problem and it would be best to have your gecko seen by a veterinarian.