Comment by ForHackernews

You could build some measure of "loyalty" into a contract:

* We train you for six months and pay you full salary.

* You have to work for us for two years past the end of your training period.

* If you leave before that, you owe us 50% of salary from the training period. (or whatever)

In a competitive market, you might even see other companies willing to buy employees out of their contracts.