Green’s Dictionary of Slang

tailing n.

[tail v. (1)]

sexual intercourse.

[UK]‘Walter’ My Secret Life (1966) IV 649: We had a game of tailing which lasted some hours.
[US]W. Brown Run, Chico, Run (1959) 9: He’d thought the guy was a dick; instead he was just another cat come up to Little Spain to do some tailing.