How do you keep a mattress topper on the bed?

So I have this big, fluffy mattress topper is that what they are even called? on my bed.. but it keeps sliding off. After maybe two or three nights, it starts to slide off the side yes, I have sheets.
I temporarily fixed it with two ace wraps tied around my bed, and that held it on for about a week, but it still slides off.

Any ideas on how to keep it on?