It's better to have continuous fencing without such corners. A gently curved or rounded 'corner' is much less likely to serve as an escape route. Fences should be of adequate height and depth. Ideally, all fences should be at least 1.5 to 2 times as high as the tortoise is long. Many species are adept at burrowing and scraping too, so it helps if all fences are dug in to a reasonable depth.
Tortoises are highly resourceful and determined creatures.
If there's a way, they'll find it. Beware of toxic substances used as wood preservatives. Use safe alternatives and allow materials to 'weather' before use. Substrates Use an appropriate substrate for the species to be housed. Desert species will require a sandy, very well drained substrate, while many tropical species prefer moist leaf-litter, moss and crushed orchid bark.