I have ornate box turtles that have bred successfully outside for the last six years. They have mostly a shaded enclosure with a few sunny spots for getting warm and they have a pond. I have several places where they can be in a tunnel - two made with rocks like little caves and three broken clay flower pots laid on their sides. They also have an area that I mixed a little sand into that they always seem to lay their eggs in. In the fall, after they dig in for hibernating, I cover the entire pen with about a foot of leaves. During the summer I water the pen down almost daily with a mist setting on my hose. Even though they have waterers and the pond to drink from they seem to enjoy drinking from the little streams that form from the misting.
Any corners you have on your pen need to be covered in some way as turtles are quite adept at climbing out of enclosures, however, my enclosure isn't covered in any other way and I've never had a predator of any kind mess with my turtles and I get skunks, oppossums, and all kinds of birds. I've even had a stray dog or two that's managed to end up in my yard somehow, but they've never hurt a turtle. The wild birds often drink from the turtle pond as well as my outdoor cats. The turtles actually chase my cats out of their pen which is quite funny to watch.
What are you feeding your turtles? Mine get a variety of fruits, boiled eggs with the shells still on, grasshoppers, worms, an occasional treat of tuna or shrimp, and leaf lettuces. I cut the eggs in half and the fruit in big chunks and put out whole pieces of lettuce rather than chop everything up. That way they have to bite and pull to eat just like if they were foraging on their own in the wild. They are huge fans of strawberries and cantalope.