Prevent user from deriving from incorrect CRTP base

Question

I cannot think about a proper question title to describe the problem. Hopefully the details below explains my problem clear.

Consider the following code

Answer 1

1) make all constructors of Base private (if there are no constructors, add one)

2) declare Derived template parameter as friend of Base

template 
class Base
{
private:

  Base(){}; // prevent undesirable inheritance making ctor private
  friend  Derived; // allow inheritance for Derived

public :

  void call ()
  {
      static_cast(this)->call_impl();
  }
};

After this it would be impossible to create any instances of the wrong inherited D2.