If you're headed outside, this can be a tough one to avoid. Use common sense. If you see your rabbit eating large amounts of dirt, stop them. Most rabbits will do fine just padding around the earth and digging the occasional hole. When summer temperatures soar, your rabbit is better off being a couch potato.
Heat is intolerable for rabbits.
If the temperature is above 85 F, postpone your excursion. Try making your trips to the yard early in the morning or in the evenings when the outdoor temperature is slightly cooler. Make sure your rabbit has a shady spot to retreat to, and plenty of water to drink. If you are traveling or underestimated the heat level, get your bunny to a cool spot as soon as possible. Drape wet towels over their cage or carrier, or freeze bottles of water and place them around the rabbit.