Depending upon how porous your rock is, you might want to think about using some sort of sealer on it, like maybe resin. At the very least, I would coat it with a few thin coats of gesso and then use your acrylic over top of that. Let us know how it goes as you experiment!

Try a base coat of white let it completely dry, then apply your red, always works for me.

I use Liquetex Basics acrylic, they’re cost effective and thick enough to coat well. The Folk Art craft paints are okay on top of a white surface but they have a lot of binder so they’re pretty thin.

Hi I use acrylics and varnish them with an outdoor varnish:)