Halloween // Help! Looking for suggestions on how to keep styrofoam tombstones from blowing over!

So I have my Halloween camping trip coming up September 17th(our local jellystone does a big Halloween event in September) and I really want to utilize my big tombstone collection this year. It's just the basic styrofoam ones you can get anywhere, but I get the bigger three foot sized ones mostly. We also repaint ours to give it that special and unique flair.

Anyway the first problem is our site has terrible ground. It's like hard rock and you have to take a hammer and chisel to anything you stake into the ground. So basically those little metal stands the tombstones come with don't do jack squat for holding them up.

The second problem is we usually have wind, don't know how we get that unlucky but yeah. The method we used over previous years was we bought a bunch of rough wood stakes from lowes, spray painted them black, and velcro'd them to the back of the tombstones. Well that worked for all of five seconds before they all popped off and we just started tying them to the stakes with string. Which looked fine from a distance but up close looked rather tacky.

So does anybody have any suggestions? Or even if they have a tutorial or something on youtube. I would greatly appreciate any advice/suggestions you guys have.