Paint question about fixative or sealant with painted rocks?

I just started painting on a variety of surfaces. I use acrylic paint. I want some of my things to be weather/uv proof. Am i supposed to be looking for a fixative? an additive to the paint? a sealant? does it spray on, brush on? I am wondering what i need for stone... like if i paint rocks or wood pieces? does anyone know about the sealant to use for painting rocks? so its weather/ UV proof? what would you recommend? Thank you!