There's a bright, clear line between targeted attempts to hire someone who has a job working for a competitor, and trying to get that person to take confidential information with them when they switch jobs. The latter is wrong and will rightfully result in legal action. The former is perfectly fine, and good for employees, which I'd wager still includes most of this site's audience despite the startup-founder focus.

Remember, employers don't own the people who work for them. They cannot be "poached." They can only be given a better offer. If your employee decides they'd be better off working for your competitor instead, then you have only yourself to blame for not giving them enough incentive to stay. Either up your game, or give them a friendly goodbye.