These two are rock-solid businesses with strong dividend programs.Every corporation will face challenges and setbacks -- which will sometimes sink its stock price. That's not a good reason for long-term investors to jump ship unless, of course, there's a fundamental shift in the company's prospects.Stocks that can perform reasonably well while maintaining a positive long-term outlook may well be worth holding onto for good. Corporations in this category are common, but they do exist; two examples are Merck ...