You're operating from the 1950s veiwpoint which is really a cultural hold over from the great depression- that employees should be desperate to find a job and companies should be free to screen them out for any arbitrary reasons. Let me guess, you make them write code on a white board too.
If you have a one year cliff you are providing a huge financial incentive for your employees to leave after a year, by shifting the risk onto them.
Maybe that's why you don't have enough people already?