@Gayla2
I don't know if you're a live in host or a remote one, but when I am saying goodbye to guests checking out, I say, "It would be great if you could leave a review when you have a moment and I will of course do the same for you."
If I don't see them on check out, I normally send a goodbye message where I thank them for being good guests and then ask the same question as above.
It's not very sophisticated and I currently have a 69% review rate, so there's obviously some room for improvement, but I think that some guests are not going to leave a review whatever you do. They just can't be bothered, especially if Airbnb is something they're only likely to use every couple of years at most. I'm happy if 2/3 of my guests review.