Millions rely on Social Security for their retirement income, but the program is under financial threat. With long-term benefits at risk, many proposals have surfaced to try to shore up Social Security's finances.

In the following video, Dan Caplinger, The Motley Fool's director of investment planning, looks at four of the more popular proposals to strengthen Social Security. Dan notes that retirement ages are already on their way up to age 67, but some believe that 68 or even 70 would more accurately reflect life expectancies. Means-testing Social Security to take away or limit benefits for upper-income recipients is especially controversial, raising disagreements about the nature of Social Security either as a safety net or as a pension benefit for all. Dan notes that Social Security payroll tax rates haven't risen in almost 25 years, making a rise in the current 6.2% rate a possibility. Finally, Dan looks at proposals to raise or eliminate the current wage base limit of $117,000, citing similar moves to Medicare taxes that boosted revenue. Dan concludes that none of these solutions is a slam-dunk winner among those looking at the problem, and all of them might well be up for debate for years to come.