It sounds like many are not following some basic tenets of encapsualtion and good design.
Keeping things isolated and unreliant on other parts is essential to avoid the problem you describe. You might need some higher level designer or architect. This is a typical scenario where people have justified some draconian processes and change management. (I do not advocate that)
You need to avoid dependencies and interrelationships and define and use public interfaces only. This of course is an oversimplification, but you will probably learn a lot by some metrics on your code - complexity of classes, public methods, UML diagrams built from reverse engineering the code, etc.
