I've seen a few responses about extra rocks spawning with extra ponds, but I'm pretty sure my town with 3 ponds has fewer permanent rocks than my town with one pond. I'm actually going to check
Edit: Checked and Cardamon (one pond) has 8 permanent rocks and Glendale (3 ponds) has 6. However, I started Glendale more than 3 years ago, where Cardamon was started after the update. Not sure if that has anything to do with it.