Being the chief executive of a public company has never been ­easy. ­Lately, it has been all but impossible. Enron-era accounting scandals, alleged ­options-­backdating misdeeds and other tawdry scrapes have ­given rise to strict new regulations, a wave of investor activism and increased second­-­guessing by no-longer-quite-so-pliant boards of directors — all of which has raised already-high stress levels and contributed to record turnover among CEOs. The ­only reliably positive news for chief executives had been a strong economy. ­No longer. Now, with housing and ­credit­ ­market crises threatening to trigger a recession, corporate chiefs will have to struggle to maintain, much less grow, earnings. And that will only give restless shareholders and independent directors more reasons to clash with the men and women at the top.“CEOs are very much on guard right now,” says Keith Meyer, co-head of the North American CEO practice at executive search firm Heidrick & Struggles...