The Staff Review Record
You should have a system for monitoring staff progress, for showing that you have addressed problems with their work BEFORE taking more drastic action. Every year a small number of ACBI members wish they had been more careful and it can cost a lot of money to ignore these procedures if a problem then arises. Not following good procedure (and being seen to) can result in a finding and damages against you.
Twice a year you should talk to each staff member, however informally, on an individual basis. Fill out the form and ask your employees to sign it. Where there is disagreement about a comment, try to resolve it, or note the employee's disagreement. But you are entitled to reach and record your own conclusion.
Repeat the exercise in six months or at a suitable time.