archer up, n. — Green’s Dictionary of Slang

archer up n.

[the champion jockey Fred Archer (1857–86) and thus phr. ‘Archer is up in the saddle’, which, to betting men, more than likely meant a winning horse]

a certainty.

[1876		Freeman’s Jrnl 20 Mar. 3/1: Old Thunder will be among the competitors, and with Archer up he will not be far off].
1909		J. Ware Passing Eng. of the Victorian Era.