Green’s Dictionary of Slang

1. (US) trouble; usu. in phr. in the dogfuck.

1978

W. Groom Better Times Than These (1979) 37: Spudhead jammed his hands into his pockets and said with authority, ‘We’re really in the dogfuck now’.

2. sexual intercourse in which entry is made from the rear.

2003

‘Rev. of Enge Teeny-Saue’ on YourChoice.co.uk 🌐 Commuter Tonia accepts a ride from a stranger and is sweet talked into parking in the woods. Tongue tweaking her small, hard nipples has the desired effect; her lips wrapped ’round his knob, a dog fuck in the boot and his spunk spurting into her mouth from his engorged, purple bell end.