What are the best ways to ensure the safety and well-being of my rabbits by providing them with a large exercise pen?

To ensure the safety and well-being of your rabbits in a large exercise pen, make sure the pen is secure with no gaps or openings for them to escape. Provide plenty of space for them to move around and stretch their legs. Include hiding spots, toys, and fresh water to keep them mentally and physically stimulated. Regularly clean the pen and monitor their health and behavior for any signs of distress.