How long can you be on depoprovera before you have to worry about thinning of the bones. I have been on it for 11+yrs?

Not sure. There is no black and white answer concerning osteoporosis (thinning bones) and the use of depo-provera -- but since the fda placed a "black box warning" on depo-provera about it's link to osteoporosis, most physicians now limit it's use to 2 years, unless there are very extenuating circumstances.
Yikes! The lack of cyclical bleeding really affects bone health as appropriate estrogen and Progesterone balance are what keeps your bones healthy. Since depo is a synthetic progestin it interferes with this balance. After 11 years you might consider having a bone density study to check, and i'd give strong consideration to a non-hormonal bc option. Have hormones tested and restored to heal bones.