I would like to suggest that around the bottom 2 or 3 feet instead of chicken wire, go with half inch metal hardware cloth - much less bendable. teach1rusl makes a good point. I also know someone who lost a duck due to a one inch gap under the pen gate.
So, really, even a one inch gap where raccoons can reach through is a security problem.
They have all night, all day to get in....
My pen sits on the ground. The underside of it is coated chain link, attached at the edges of the pen. I have a mix of duck manure and chopped straw and leaves as the bedding, and the pen is on a 2% slope so it drains.
That is really important - drainage - some pens are too level, or have low spots, and that holds water and increases risk of disease.
Some folks use stall mats over concrete. Those you can rinse. I feel that ducks really appreciate something a little more natural that will absorb their manure. Because if they are on stall mats, they are walking through their poop until the next rinse-off.
But definitely cover the concrete, because bumblefoot occurs more often when they are on that kind of surface.
I have woven wire fence across the top of the day pen, and in winter I have covered the top with heavy row cover fabric (I can get it in 12 by 20 ft size).
When I have done that, I have made myself another chore, because when one gets 18 inches of snow over night, first job in the morning is getting that off the top of the pen before more snow falls, and before the ducks go in there. Snow load is something to consider.
But if you're in Florida, maybe not so much!