The popular design pattern MVC (Model/View/Controller) has an extended cousin MVC-ARS (Action/Representation/State). The added components all live within the database layer
Never underestimate the ability of a developer to bastardize whatever safeguards you think are in place. While these added separations may allow for additional protection, do they make it easier to develop? Do they make the separations easy to understand and use? If not, the developers are less likely to incorporate them into their practices.
Developers tend to work towards the least resistance.