With the S&P 500 index recently hitting a new all-time high, we can officially declare that we are in a bull market. While that's exciting news, it doesn't change the blueprint of success for long-term investors. The plan remains to pick out stocks to hold on to for a while, stocks that can perform well in good times and stay in one piece during bad times.For investors in search of such companies, let's consider two excellent candidates: Merck (MRK 0.57%) and Fiverr (FVRR 0.57%). Read on to find out why the ...