I use a 10' guyline on the head-end, opening-side, tarp corner; I can prop that corner up with a stick (porch mode'ish). And use 6' guylines on the other three corners of the tarp.
To attach to the tarp's corners, I use 2' of line and make it into a loop using a double fisherman's knot. . .use a prusik knot to attach each guyline to a the loop, and larkshead the loop to a corner of the tarp.
This gives me an adjustable line on each corner without needing any hardware.