Looking for a stock to hold for the majority of one's lifetime can be fraught with peril and uncertainty. The only constant is change, and it can be difficult to anticipate how changes will affect any investment in terms of quarters and years, let alone decades. While there isn't any investment that you can buy and simply forget, there are some companies that increase the likelihood that they'll still be in your portfolio in 50 years' time.With that in mind, we asked three Motley Fool investors to choose top companies they believed could still be viable investments come 2068.