It's a difficult one to search for. I checked old newspaper archives but nothing came up. The best information I've found is a forum post with thorough research by Ken Greenwald, which I'll post.
Greenwald didn’t find it in fullany historical newspapers, magazines or journals but did find it used in case of future linkrotsports circles such as mountain and bitrotrock climbing, starting in the 1990s. It may have been passed from sailing due to the connection with rope: there may a further connection to the nautical ‘pulling really hard on a halyard'.
Dana, YARD ON IT is a puzzling phrase. I did a pretty good search and didn’t find it in any historical newspapers, magazines, journals, etc. But I did find it in use starting in the 1990s in books and on the web (see quotes below), and clearly with the meaning you suggest, ‘pull really hard.’ The term seems to be popular in various sports circles, especially mountain and rock climbing. And the rope connection would fit in pretty well with being passed to us from sailing.
The only thing that I could find in the way of a verb usage in a slang dictionary was “To inclose (cattle, etc.) in a yard. Also with up” from the Oxford English Dictionary (OED) and “To ‘corral’ or ‘round up,’ to get hold of: Canada: since late 1950s” from Eric Partridge’s A Dictionary of Slang and Unconventional English. Partridge’s ‘get hold of ’ is close, and Canada is close to Maine, but 'get hold of' isn't quite 'pull really hard' and you make it clear, as do the quotes I found that it does mean exactly that, and the nautical ‘pulling really hard on a halyard' explanation does sounds reasonable.
He got in touch with DARE:
<“The only remotely similar thing I found in a quick check is this: 1949 in 1965 DARE File Ann Arbor MI, "If anyone takes my drink, I'll yard him with a necktie." Informant. . . did not remember where he had picked up the expression, but [it] means vaguely 'to hang.' Probably from expression 'to hang from the yard arm.'“>
So, the source of your expression remains a mystery except for the outside possibility that it evolved from the 1950s Canadian ‘to get hold of’’ mentioned above.
<1997 “ . . . on the C-53 you must pump a large, beefy three-foot-long arm 30 or 40 times to set or retract the landing gear. You have to YARD ON IT pretty hard, too, for it isn't as easy as jacking up a car.”—‘ Dakota Squadron ...Travelogue Day -1,’ http://aztec.asu.edu/dakota/day1.html, 22 June>
<1998 “If the nut is buried deep in a crack, you may have to really YARD ON IT. Be warned
that this can bend any cable which, done repeatedly, can not only ruin the nut’s symmetry but weaken the cable . . .”—‘How to Rock Climb’ by John Long, page 88>
<2000 “It's pretty well attached and stretches some so as not to break if you catch it on something in a minor way but will actually come undone if you really YARD ON IT.”—‘Best Location on Octopus’ [[scuba diving]], http://groups.google.com/group/rec.scuba> 28 February>
<2004 “I think I may have cracked the window on a door to Covell Hall. It gets stuck and the only way to get it open is to YARD ON IT, hard. So I did and then I looked up and there was spiderweb-like cracks. But I don't know if they were there before."—http://www.ahqt.com/by/2004_12_05_archive.html >
<2005 “You already know that the stuck rope will sustain your body weight should you attempt to prusik up it or YARD ON IT when you need to . . .”—‘The Mountaineering Handbook’ by Craig Connally, page 165>
<2005 “This one hold just kept crumbling when you grab it, and it feels like it moves when you YARD ON IT . .. but I think it'll hold, for now.”— http://www.tracstarr.com, 17 August> [[rock climbing]]
<2006 “The boot flexes quite a bit when we YARD ON IT, but it flexes the same for each test so it gets cancelled out of the results.”—“Flex Testing a Backcountry Skiing Binding,” http://www.wildsnow.com/?p=380, 22 August>
Ken G – October 3, 2006
See his full post for much more.