...
public:
...
     // query owned flag
     bool IsOwned()const{ return owned; }
     Ctrl& Owned(bool b=false){ owned=b; return *this; }

...
};

class App: public TopWindow{
...

App()
{
   Button * p  = new Button();
   Button * p2 = new Button();   

   this->Add(p.Owned());

   this->Add(p2); // Error, p2 is not owned.

   // fixed p2;
   p2.Owned();

};