I find a nice piece of cardboard or foamcore a little bigger than the block. I place the block on the board and using a fair size sewing needle and crochet cotton thread, put a stitch going through the seam allowances in the 2 top corners and knot the thread on the back. It secures the 2 top corners to the board and allows the judge to flip up the block to see the back. Make sure all your seams are pressed nicely and all threads trimmed. I use a hole punch to put a hole in the edge of the board to attach a tag to. Your fair will give you a tag to put on it? With that bring said, this is the way we do it in my area, yours might be different.