If you want to keep people give them a compelling reason to stay. Collusionary practices like anti-poaching, Noncompetes and so on are not fair and just. They are immoral and bad for the markets. Engaging in any of these practices should come with hefty fines.
This isn't about an unhappy employee leaving because the job is crappy. Of course not. If the job or the environment is crap I'd be the first one to say that they probably ought to leave.
I am also deeply offended by your use of the term "slave". Nobody has used this term. Not one person has even implied it. I certainly have not. It is a despicable and desperate measure to sensationalize something that has, in no way whatsoever, implied such a condition exist or is desirable.
My post, and the scenario that it referred to, was very narrowly focused on the case where an agency YOU HIRE to help you find talent turns-around and proceeds to attempt to poach the very talent they helped you find just a few months after they got onboard. That is scummy and, in my view at least, absolutely justifies a no-poaching agreement WITH THE AGENCY YOU HIRED TO HELP YOU FIND TALENT.
Other than that, if another company is going to reach out and offer your employees a better deal (whether that means more money, a more interesting project or better working conditions) so be it, that's the free market and nothing should impede that at all. Even if other agencies reach out and convince the employee to leave a week after he/she came onboard, that's OK.
Again, the point here is very narrowly defined around the issue of a head-hunter that YOU hired turning around and poaching employees you just got done paying them a fee to find. That is a very different issue, isn't it?
In order to fully illustrate the damage done I simply highlighted that there are huge costs involved in hiring and employing someone, particularly through a head-hunter, and that it is wrong for them (the head hunter) to then turn around and try to steal people away from you.
After a reasonable and mutually agreed-upon period they can do whatever they want. In the example given in the OP's article that period was 18 months. That's fine.
To be ultra-redundant: If someone other than the agency you hired manages to pull someone --anyone-- away from you, that's fair game. You can do that to others as well as they can do it to you. The issue here is with an agency that is supposed to be working for you.
When I read slave I immediately jumped to 'Wage Slavery' http://en.wikipedia.org/wiki/Wage_slavery and it happens all the time. People cannot leave their job or risk looking for a new one because they are living pay check to pay check.
That is what I took away from that statement.
They don't know and they don't care who they've placed where (at least the part of the company that sends out these "poach" emails doesn't). A new employee isn't going to jump ship within a month of getting a new job unless a) they really hate the new job or b) the new offer blows them away to the point of being willing to burn bridges.
I suppose agencies could put some kind of filter in their DB to not let people under no-poaches show up in the results, but why bother? Every company probably has a different no-poach period and all kinds of bothersome clauses they want and it nearly never comes up anyway so it's not worth the effort to deal with the issue. It easier to worry about these things on an exception basis, e.g. employee answers back with interest. At this point we can check if there is any reason we shouldn't go forward. But they will be sending out so many emails, most of which will be ignored, there's just no point thinking about it until someone actually answers.
This is simply a classic case of assuming there is malice where in truth there is just laziness.
Six month later I get pinged by a large corporation looking for a CFO. I remember the candidate I placed with you. She is definitely qualified. I email her directly and get her to jump ship. She didn't get paid any more. I simply convinced her that the large corporation was a better bet than your startup. I, of course, get to collect a fee from the large corp as well.
This is wrong. You hired me to help you build your team and paid me handsomely to do my job. If I then turn around and actually become your enemy, why am I serving? An even such as the one I just described is incredibly disruptive and costly beyond the obvious (I covered some of the costs in my prior post).
That why I will not work with any head-hunter who will not guarantee that they will not approach new hires with new opportunities for a reasonable period of time. As a business you don't derive a financial benefit out of hiring a new employee for months but there's a ton of upfront and ongoing investment.