Put heavy duty stakes underneath them and stick them into the dirt.
I glued down the tombstone on gray painted plywood and have never a problem
hope this helps: https://www.youtube.com/watch?v=Dx9LnCME6f4" target="_blank">https://www.youtube.com/watch?v=Dx9LnCME6f4
I glued paint stirrers on mine and they’ve been solid for two holidays. Good luck!
*I spray painted the paint stirrers dark gray so you can’t see the big ‘Lowes’ on them