Positioning / Distributing Prefabs in an environment

Hi Everyone,

I have a simple terrain on which I am modeling a simple VR experience. I want the environment to be covered in rocks, and the unity asset store has many fantastic prefabs. What is the best way to distribute these prefabs (and their duplicates) across the environment?

I understand that you can use the Tree tool for terrains, but because I can only set density, I end up with way too many similar rocks in a tight area.

Any advice would be greatly appreciated.