Threats mean you're passionate. Threats mean you care.
You can't have a handshake deal between companies agreeing not to recruit from each other without running into anti-trust issues. So that approach is problematic. But, you can be direct and indicate there are... um... consequences for poaching your most talented people.
Last week I put a call out for candidates on a great HR leadership spot in Houston - at Cimation (click the link for the job posting). When the post went out to email subscribers that day, I got the following reply from a leader of a company who is a Capitalist reader, and knows that their HR leader reads the HRC as well. Here's what that leader had to say:
"l'll break both your legs and have every basketball hoop removed in a 50 mile radius if you even think of Julie."
Julie's not her real name. But that's my kind of leader. Physical health - check. Attack the passion - check.
I like passionate people. Passionate people don't sit on the sidelines and become victims. Passionate people take action. They are clear. Crystal clear.
I have no interest in Julie. That is all.