Percentages. Some percentage in a CD. Some percentage in corporate bonds (BulletShares ETFs are good for your purposes). Some percent in a lower-volatility i

Percentages. Some percentage in a CD. Some percentage in corporate bonds (BulletShares ETFs are good for your purposes). Some percent in a lower-volatility index ETF (say dividend-yielding stocks -- DVY being an example). Maybe some percentage in a lower-volitility ETF (say dividend-yielding stocks in developed non-US markets -- IDV being an example). You might also consider things like US Treasury bills and notes, for the tax advantages.