NEW YORK ( TheStreet) -- Congress could raise taxes next year, so this is a good time to prepare for the worst by making maximum use of the shelters offered by IRAs, 401(k)s and other retirement accounts. Earnings from sheltered assets can compound tax-free until you take withdrawals.If much of your portfolio must remain in a taxable account, then you will have to decide which assets to shelter and which to leave out in the cold. Your aim should be to protect those investments that generate the biggest tax bills. Among the most tax-efficient holdings are stocks that pay no dividends. If you own such shares in a taxable account and never trade, you can postpone paying taxes indefinitely. But if you tend to trade rapidly, then you could generate short-term capital gains, which are taxed as ordinary income at rates of up to 35%. To avoid big bills, heavy traders should keep stocks in a shelter. VTSMX), which has a tax-cost ratio of 0.29. A candidate for a shelter is Vanguard Mid-Cap Value Index ( VMVIX), which has a tax-cost ratio of 0.72.