Any way to make a entity walk on water? (by replacing it with stone)

If you seen the broken script or the knocker and how the entities can turn the water into stone to walk on it, that's what I want to know how to do. I've tried this  using procedures+

But the filling doesn't work that well and only 1-2 water gets turned into cobblestone AFTER the monster falls through it.

Its also using an on entity tick event.