The heat and the sun are very stressful to bunnies and can kill them. Provided shade (and a box for hiding) and allow to play during mild temperatures only (approx. 45-80 degrees). A dog exercise pen at least 36" tall with in full or partial shade would be best, when having the rabbit outside. Don't let your bunny play on grass that has been treated with chemicals. As the chemicals can be bad for them! Be mindful of predators such as hawks, dogs, raccoons, etc. 1 to 2 hours of exercise outside per day is plenty.