I've been thinking about this and have a couple suggestions. A little backround first...I survey for a living and I can tell you that a 12" long 1.5"x1.5" stake pounded in flush is a real bear to pull out. You need to dig it about half way, then wriggle it pretty seriously to get it to come out. That being said, try this:
Use a cable that is about the same length as you wood stake (at least 12"), with loops at each end. Place the point of the wood stake in one end loop (make sure the loop is smaller than the wood stake), then drive ththe stake/cable into the groun-flush. Attach your trap chain to the other loop. Use a swivel right there where you connect. That stake will not come out. With the lateral pressure put on by the Coyote(the pressure will be put on the point (bottom) of the stake, not the top), the stake will act like a large earth anchor type stake...won't move the top of the stake and loosen the hole as someone mentioned before.
That should solve the 'how to connect' and 'enlarge the hole' questions. I would feel comfortable using an 18" 1"x1.5" stake as well. All you'll need is a 3 pound hammer in most cases. Longer stakes will work in sandy soils. Better use rebar if ground it frozen.
Hope that helps...Ken
HEY YOU DANG WOODCHUCKS, QUIT CHUCKIN' ALL MY WOOD!!!!