How to define more than member of Un-named namespace outside?

Question

When it comes to using namespaces it is really good thing to avoid name clashes. But the thing that matters me: Using anonymous namespaces.

Here in my example for some reason I defined two un-named namespaces and accidently the two has a member function with the same signature. And I want to define the two outside the namespaces.

namespace {
    void foo(); // to be defined outside in somewhere else
    int x = 0; // I want the above foo() to increment x
}

namespace {
    void foo();  // to be defined outside in somewhere else
                 // I want foo to do something else
}

// Here is my guess how to define a function outside Anonymous NS.
void ::foo() {
    cout << "::foo()" << endl;
}

// void foo(){
//   cout << "foo()" << endl;
//}

int main(){

    foo();
    ::foo();

    cout << endl;
    cin.get();
    return 0;
}

• How to avoid name clashes when having multiple Un-Named-Namespaces?

Thank you.