Dude, screw the ring, give your girl an AR-15 with a halo sight that shoots 600 rounds per minute... If it's meant to be she will say yes, if it's not... well then you'll still have your AR instead of some shiny rock.
Only tricky part would be where you could propose and somehow pull the AR out of your ass when you get on your knees..
Im pretty sure my girl would appreciate an ar more