Subject: How does one determine the sex of red-backed salamanders?

Through internet research, I have not been able to find a method of 
determining the sex of red-back salamanders while out in the field.  Is it 
only possible to determine the sex of salamanders by dissection?  It would 
be helpful to gain sex and age ratios of the salamanders in a population 
study, but is it possible?  There was one guideline that I found on a site 
in New Brunswick stating that measuring the body may determine sex; however 
these measurments were female (7-10mm) and for males (6-9mm).  Not too 
helpful really.  The salamanders that we did catch this spring were 
measured (a tip of nose to tip of tail, and also tip of nose to end of 
cloaca measurment), and fell within the rather broad aforementioned 
measurments.
If anyone should know a method of sex determination that can be performed 
in the field, it would be greatly appreciated.

Re: How does one determine the sex of red-backed salamanders?