Place the ground beef in a large pot with garlic & onion. Cook over medium heat until browned. Drain off the excess fat and add to slow cooker. Add tomato sauce, chili powder, cumin, oregano, salt, Rotel and cayenne to slow cooker. Stir together well, cover, and cook on high for 2-3 hours or on low for 4-6 hours, stirring occasionally. If the mixture becomes overly dry, add water at a time as needed. If it’s too watery, thicken with cornstarch dissolved in a little water.