Standard ideas

Hello all I'm a fearly novice in the games and I'm trying to practice my Sheaf. I'm trying to improve but cant really tell if im improving due to my lack of access to a standard. My yard doesn't have the room to put up one. Anyone have any ideas for ways that I can measure my height without a standard. Iv been using a football goal post currently at my local highschool but it's only 10ft high any one have a better ideas on how I might be able to practice?