Question about fossils in landscaping rocks

Hey there, I've seen a lot of posts around of people finding fossils in landscaping rocks. Now when I see rocks in peoples gardens at the edges of the sidewalk I have to hold myself back from digging around lol. Is there a specific kind of these rocks that generally have more fossils? I've heard about "river rocks" but I'm not sure if those are composed of different rocks than normal landscaping rocks. Some landscaping rocks are raw and jagged looking, while others are smooth and round. I would think the round ones would have less fossils.... maybe because my garden has the round ones and I've never found any.