How to detach python reference from c++ pointer?

[lianera]

If a python object is gained from c++ function return, which may look like this:
c++ define

class A
{
public:
    static A* Create()
    {
        A* a = new A();
        /* some auto instance manage code*/
        return a;
    }
};

PYBIND11_EMBEDDED_MODULE(t, m)
{

    py::class_<A>(m, "A")
        .def(py::init<>())
        .def("Create", &A::Create, py::return_value_policy::reference)
        ;
}

and python

from t import A
a = A.Create()

This function using py::return_value_policy::reference, because the lifecyle is managed by c++.
When c++ is about to delete the pointer, how to detach it from python object or some way to disable python object? So that python object won't use c++ pointer anymore, to prevent crash.
I am porting a large library to python, so it is not convenience to change the original instance manage way to smart pointers.
Also, it is possible to find python object which hold the c++ pointer?

[lianera]

Problem still not solved, it's there any suggestions?