How can I keep someone on my Facebook friends list but keep that certain person from seeing my posts?

[Lenny]

You can add this certain person to your "Restricted List"

What happens when I add someone to the Restricted list?

When you add someone to your Restricted list, they'll only be able to see your Public content or posts that you tag them in. So if you put your boss on your Restricted list, post a photo and choose Friends as the audience, your boss (and anyone else on Restricted) won’t see that photo. However, if you add a tag of your boss to the photo, we’ll let them know they’re in it and they’ll be able to see the photo. If someone else tries to tag your boss in one of your photos, you’ll get to approve this tag from your pending posts.