Hi Paul,
I live in an area with groundhogs, skunks, foxes, racoons and even on occasion bears around (no, I don't live in the wilderness at all, but this is Canada and a huge, kind of national park, is 'around the corner').
But just the racoons alone are the worst trouble in that respect. An adult racoon won't have any trouble to carry away any of your torts and hurt / eat them, or just 'play' with them. They are amazingly inquisitive and have a lot of patience and skill to get into almost anything they are intested in. And,- they are interested in almost anything.
So in my opinion there is no way to keep these torts outside in an enclosure, that is not racoon proof.
This friend of mine, who has a big group of adult redfoots in the 30 cm plus SCL range has solved this problem by building a 2 m high privacy fence around his property and putting an electric fence on top of this privacy fence. And while they probably learn, he regularly hears racoons whining, that hit the fence. On top he built a heated shed for the torts, where they are getting locked in for the night. He even has the flap door to the shelf on a timer, so it can open by itself at a certain time during the day, when the mornings are still cool, but he has to go to work. But for the night this door is really locked.
So it is really important to consider the abilities of racoons,- they are amazing (unfortunately...)!
Gaby