<p>How can a .net class library project and resulting dll be protected so it cant be referenced by other applications (.net projects) except those projects in my own solution?</p>

Forgive my ignorance, but if they're all class libraries, what does the code do?  Isn't the purpose of having a dll so that the code can be referenced.
In any case if you mark everything
```
internal
```
it won't be able to be accessed outside its own library