Tie grass bundles to lay across the opening, and make more than it takes to just cover the pit, so it will always be easy to pull them overhead and leave just slits to watch birds work through. Big bundles 4-6" wide at the ties with two ties in the middle will last longer, but small bundles half that size and only tied in the middle will look more like random grass on the levee and less like grass logs. If the levee is clean, you'll want to cover enough of it with cut grass matching your bundles to keep the blind from being the odd, suspicious spot.
This pic was posted on the similar thread right below this one, and dog and decoy are sitting on the end of the blind:
Here's are other exampes:
If the levee is green, you'll want to use cedar boughs, instead, as seen on the blind behind this hunter:
If you think I'm wrong, you might be right.