stack-guard

from The Century Dictionary.

• noun A covering for a haystack or rick, whether for the top or the exposed side. Sometimes it is suspended from posts temporarily set up.

from the GNU version of the Collaborative International Dictionary of English.

• noun A covering or protection, as of canvas, for a stack.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A covering or protection for a haystack, such as a canvas.