I found this in "The Anti-Nicene Fathers" published by Wm. B. Eerdmans Publishing Company, Volume II "Tatian's Address to the Greeks" p.66 "And who would give his approval to the cynogamy of Crates, and not rather, repudiate the wild and tumid speech of those who resemble him...."
dog coupling. related to the Ancient Cynics ("cyn") who were fine acting like animals, like dogs, in public - wanted to break down the public/private dichotomy and be close to nature like dogs. even public sex, fucking like dogs. I am vaguely recollecting this so don't take my word for it.
wanted to check this out. some googling shows this word was probably coined by Cynic philosopher Crates, in reference to his marriage; both husband and wife were of the Cynic school. So it sounds like he was simply saying it was a "marriage of dogs", or of dog-like people, in other words, of Cynics. I don't think he was trying to connote retrocopulation. "Marriage" is a stronger translation of the Greek γάμος—gamos—than "coupling" (indeed, the IE root *gem(e)- is supposed to be "to marry")