Green’s Dictionary of Slang

1. (Aus./N.Z.) a voyeur, esp. one who spies on couples in the open air.

1902		Bulletin (Sydney) 15 Nov. 10/2: The sudden death (per bullet) of Lancer Haines in Sydney Centennial Park has aroused a widespread public interest in the business of ‘foxing.’ Most people have a fixed impression that the foxer is always a blackmailer.
1905		Sun. Times (Perth) 12 Mar. 1/1: The blackmailing foxer is largely in evidence in the West Perth parks [and] a number of numbskulls have paid toll under threat of being ‘exposed’.
1913		Sport (Adelaide) 20 Sept. 5/1: J D, the night foxer, has a pair of night glasses .

2. (Aus.) a detective.

1907		Sun. Times (Perth) 11 Aug. 4/8: But though an aroma of the slums they shed, / The foxers failed to find ’em.
1912		Sport (Adelaide) 15 June 14/1: They Say [...] That Shan is getting in good work with Milky. Look out for the foxers, Shan.