1. Heat the oil in a large pot over medium heat. Gradually stir in the flour to make a roux. Cook, stirring constantly, until the roux is a dark brown color, about 20-30 minutes.
2. Add the chopped onion, bell pepper, celery, and garlic to the roux. Cook until the vegetables are tender, about 10 minutes.
3. Stir in the sausage and chicken, and cook until the chicken is no longer pink, about 10 minutes.
4. Gradually stir in the chicken stock. Bring to a boil, then reduce heat and simmer for 45 minutes.
5. Add the okra and cook for an additional 15 minutes.
6. Season with salt, black pepper, cayenne pepper, and Creole seasoning to taste.
7. Serve hot over cooked rice.