What is the easy way of checking the sex of a Sand Boa?

  I have two Sand Boas that are no more then six months in age. Currently eating small/medium pinkies. I have been told/or read that you can feel for small lumps after the vent. I can feel something on one, and not on the other. I also read you can tell by the tail length, but that would take a little longer as they are young. Probing is not an option at this time, cost of a certified vet and time being in the military. Any wisdom please , even though a professional seems right
Try playing a porno for them! If they're glued to the glass then they are male. If they ***** at ya about why you own so much porno, its a female ! Seriously though, probing is about the only sure way to tell outside of popping the hemipenes. Whichever you choose, make sure the person is reputable and skilled as it can damage the organ if not done correctly.
You need to take it to a herp vet. They have to probe, and if not done properly can result in death.
You could look for an experienced snake breeder in your area ... probing is the only sure way to know.