Rocks sometimes hard to see
Rocks are the main reason a run could end, but sometimes they are undistingueshable from the scenery, especially when they are hidden behind trees or among houses.
Most simple fix would be to ensure they don't appear near background or foreground scenery.
We could have other ways to make them more prominent. For example, by making them bigger, have a special recognizable shape (especialy useful during night), having them only appear on special rocky terrain (grey patches of rock formations).