Need help to prevent duplicat post

I have a list of Officers (Column B), and they have to cover a designated post on our sales floor . I wanted to random select the post for the officer and give them there post each morning. , I got the random working, the problem is duplicate post on the same person. right now I have to record the current post and compare to the new generated one and re shuffle until there all different.

I removed the actual names and post in attached files.

any advice would be great.