If your tortoises are larger than about 6 inches I don't think there is much that will bother them. Maybe a racoon if you have a lot of them but otherwise no. I have never had a problem and we had 'coons at one house that we lived in.
You did say that there will be a fence to keep dogs out. That is a very good idea. I would also keep a low profile too to keep nosey kids away. But that can also work against you....I had lost my best breeder male last year after Hurricane Frances had damaged part of my fence that I hadn't noticed. The people across the street found him walking down the sidewalk and thought he was a native gopher tortoise. They let him keep going and I never saw hime again. That was some loss I can tell you. But they didn't realize that I even had tortoises and only found out when I posted photos of him up and down the street.

Will send my new e-mail address