18 months? Little to no coverage on the rocks. Mostly frags. Probably not an ideal setup for any anemone. Defiantly not a Magnifica.
About the only option would be a run of the mill bubble tip that you can get from most online vendors with a decent history. Search here, or on the web, plenty to choose from. Just go with a basic rose or green - nothing fancy since you are in the "try" bucket.
Protect power heads as they wonder.
Already noted above by someone, but they will move until they find a spot "they" prefer. You can't force it. Also as noted it may not allow the clowns to host and the clowns may not try.
BTW - not a fan of the try part. Don't try, do. If you are not ready for do, then don't. I do not mean to sound direct but really this hobby is about caring for animals.