If your 18 go it alone. Your an adult and it's time to buck up! You could mention your parents to put a reference for the landowner. Have a card with your name and contact # on it and if your refused thank them humbly and hand them the card and ask them if they change there mind to call. If they give you permission make SURE you check in w/ them and remember them during/after season and at Christmas with a gift. Make sure you check back in early the next year to renew your relation. Getting written permission helps if you run in to other hunters or family members.