German pension (Frankfurt)

Does anyone here make voluntary contributions into their German pension account? Given the tax rate here, the fact that the contributions are tax-free makes it a tempting idea, but I'm not so sure about my ability to draw on it later on when I'm retired. I only intend to live in Germany for a year.

Other than that, what are others doing about retirement savings? Obviously I can't contribute to a Protected content , and since foreign earned income can't be invested in an IRA, I'm not aware of any other tax-advantaged options.