Used a jigsaw to cut the 5" notches in my 2 foot 1 x 6 inch.
Then glued and screwed the notched boards into the backing boards.
Then screwed the backing boards into the arena wall
Two-inch lumber would be sturdier for sure. I just had 1-inch lumber lying around and it's easy to cut with a jigsaw. I literally made these in about half an hour.