Loose lips sink ships, as the saying goes, but the truth is that debt sinks far more financial ships than loose lips do.

It only takes a business downturn or a misjudging of the potential of an acquisition, and companies can find themselves scrambling to sell assets to pay debt and negotiate with bankers.

For the investor to whom financial stability is of paramount importance, I recommend these three companies:

CSL Limited (ASX: CSL) – yields 1.65%, interest cover of 32 times

CSL is a vaccine and blood product researcher. Over the past decade its built an enviable track record of growth via acquisitions, share buybacks, and its own research & development. In fact, some of CSL’s products just coming to market now were first conceived a decade ago, showing the kind of long-term company this is. CSL does carry a lot of debt but it has huge free cash flows and its earnings cover the interest payments on its debt by 32 times – which is a more than secure level of coverage.

Although I wrote recently that CSL shares looked expensive, they’re down substantially since its results and if I was looking at holding shares for 10 years, I’d be comfortable with buying today. A very reliable dividend stock with long-term growth potential.

Blackmores Limited (ASX: BKL) – yields 3.3%, interest cover of 80 times

Blackmores sells vitamins and health products through Australia and recently into South-East Asia, which has driven huge increases in its profits and thus its share price. Yet shares don’t appear to be overly expensive today at around 22 times underlying earnings, and the company is bolstered by a very strong balance sheet. Blackmores will probably take on additional debt in the coming years as it expands further, but this should also bring further growth and is unlikely to reduce its interest cover to levels which might cause concern.

Perhaps not the first company that comes to mind, yet Blackmores offers reliable dividends, good growth potential, and financial security.

Medibank Private Ltd (ASX: MPL) – yields 4.3%, zero debt

I recently wrote that I still wasn’t keen on Medibank, despite its recent fall in prices. However, for an investor willing to look through the company’s woes and back CEO Craig Drummond’s turnaround strategy, the company has a number of appealing attributes. The health insurance industry in Australia is highly regulated and appears likely to continue delivering growth in the form of mandated premium increases every year. Demand for healthcare isn’t going anywhere, and additionally insurers are able to reinvest premiums that lapse into equities and bonds to generate additional wealth over time.

Profits can be lumpy, but with no debt and a reliable source of earnings, Medibank is a suitable investment for investors worried about the reliability of their income.

Of course, wanting security doesn't always mean you have to give up opportunity. In fact, one well-known investor made 100x his money at a time when most people are starting to think about retiring!

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Motley Fool contributor Sean O'Neill has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.