You must provide warmth and plenty of it, a VitaLite, and plenty of fresh food. A place to hide is VERY important to their well being. In the summer, outdoor housing is best, but they must be protected from dogs and raccoons and possums. Make sure they have a secure structure to retreat into at night and make sure they are in it and not sitting out every night. Install an electric fence if necessary, to keep out the predators.
Cats are usually no problem.
The tortoises are very fond of grazing and must be allowed to do so every day during the spring, summer and fall. Grass is the number one food, so don't ever spray with fertilizer or insecticide and warn your neighbors not to spray anywhere near your yard. If you catch them doing so, bring in the tortoise and thoroughly hose down every inch of your property with water. You can also try Pretty Pets Large Tortoise Food. They seem to enjoy this product altho don't overdo it.