"plastic" alternative to concrete for fence posts?

[terracore]

This product sent me down the rabbit hole of internet research. I'm drilling holes in rock that are barely bigger than the fence post. It doesn't wiggle around enough to be worrisome in fact some times I need a post driver to get it in. The type of spray foam (Great Stuff) that we're used to might actually be sufficient. They have landscaping and pond/stone varieties I need to look at. Worth an experiment I guess.

"Something I like about concrete is I can break it off the pole and reset if needed. I'm not sure if that is possible with this stuff."

You can melt it with acetone.