So, make sure there are no better offers out there. If you think your employees are going to leave after you train them, that's a problem you can solve.
The proper solution to this is to offer stock options that vest over several years to keep the employee, and to continually offer new set of options each year.
If the equity is liquid once vested (i.e. public company), then "stock I get in the future" is no better a reason to stay than "salary I get in the future". It's identical to normal compensation. If I make M a year and expect N in stock to vest next year, then I could just go out and look for an offer better than M+N.
Options that are not liquid, however are a different kettle of fish. Mentally, I will usually value them at close to zero when comparing with other job offers (because more often then not that's what they'll end up being worth).
Outside the valley nobody cares about stock options. Even within the valley many people are aware they're a gamble at best. You're most likely not working for the next Facebook.
Yes, but you have already invested money into them by hiring "green" (underproductive) workers. Someone else didn't have that burden so it's easy for them to pay a bit more to get the trained worker.
So everyone is trying to get this trained worker "ready to hit the ground running".
1) Very few candidates would leave a well paying job where they are constantly learning for a bit more money. I wouldn't leave my current company for less than a 20% raise.
2) A well trained productive employee is worth much more than market rate. However, due to information asymmetries the market is rarely going to pay them even 20% more than average.
Combine 1 and 2 and you see that all a company has to do is offer 20% over market rates and offer in depth training etc and they will have great retention.
Get creative. Admittedly super-simplified example: Would you find it sensible to hire someone inexperienced at 70% of market value, with a written guarantee to increase him/her to 110% after (let's say 6 months of) training? After 2.5 years, you've gotten 2 productive years out of him, and you have paid him (total) the same as you'd have paid an instantly productive person for 2 years. And they're not going anywhere because they're making more than market rate.
for most positions training a "green" hire is probably like 20% new, transferrable skills (PLs, frameworks, etc.), and 80% highly specific, and less broadly applicable domain knowledge. That includes things things like figuring out your process, or even who to go to for what. Besides, the best employees probably are the ones that want to learn new things, so if you land the perfect candidate that doesn't need any "training" he might be more likely to leave since he's probably doing the same "boring" thing he was doing at his last job...
