Date of composition of 2 Peter

The date of the composition of this letter has proven to be very difficult to determine. Taken literally, it would have been written between 65–68 CE because Peter was martyred around 68 CE by Nero.  Peter referenced his approaching death in 2 Peter, chapter 1:14.  He also referred to some Pauline letters that might have been written in the 50s CE.  How do you date letters?