Honestly, we've never encountered this problem. I've never poached someone that didn't work out. Usually, if I poach, I have to pay a premium so I'm fairly sure they can do the job.
We usually hire people unhappy in their current position and make an appealing offer. The chance that switching jobs may not work out is a chance all employees at all companies take. We don't do anything specific to protect against that like 99% of employers.
