static string constants in class vs namespace for constants [c++]

I want to declare string constants that will be used across various classes in the project. I am considering two alternatives

Option 1:

#header file 
class constants{
    static const string const1;
};

#cpp file

const string constants::const1="blah";

Option 2:

#header file 
namespace constants{
    static const string const1="blah";
};

Just wondering what would be a better implementation.

Already looked at

Where to store Class Specific named constants in C++

Where to put constant strings in C++: static class members or anonymous namespaces

UPDATE:

Option 3:

Based on the suggestions from "potatoswatter" and "sellibitze" i currently have the following implementation?

#header file
namespace constants{
    extern const string& const1(); //WORKS WITHOUT THE EXTERN  ***WHY***
};

#cpp file
namespace constants{
   const string& const1(){static string* str = new string ("blah"); return *str;}
}

I'm including the header file where i need to use the constants. Are there any major cons of this implementation?