Not much makes a general counsel's heart sink more than an allegation of insider trading against one of the company's top executives.

Especially when a charge comes from the Department of Justice—which unlike the Securities and Exchange Commission has the power to bring criminal cases and put people in jail—the fallout can destroy careers and reputations.

But the bad news for GCs and in-house legal teams is that making the call on which executive trades are above board and which might run afoul of the law has always been tough—and is getting even tougher.