Issues with Multiple Declarations gcc

I am attempting to use Nanovg in my OpenGL project and am getting repeated multiple definition errors such as

CMakeFiles\http://ift.tt/1oov50l: multiple definition of `nvgCreateGL3'
CMakeFiles\http://ift.tt/1q5SdT2: first defined here

Game.h

  class Game {

    public:
      void Run();
      Game(std::string Title, ScreenMode ScreenMode, int Width, int MSAASamples, bool VSync);
    private:
      GLFWwindow* Window;
      NVGcontext* VGContext;
      std::string Title;
      ScreenMode Mode;
      int Width, Height;
      int WWidth, WHeight;
      int FBWidth, FBHeight;
      int MSAASamples;
      bool VSync;
      bool Exit;
      float PixRatio;
      void Process();
      void Render();
      void KeyCallback(GLFWwindow* Window, int Key, int Scancode, int Action, int Mode);
      void SaveScreenShot(const std::string* Path);

  };

Game.cpp

//various #includes .. (STL GlaD, GLFW)

#ifndef NANOVG_INCLUDED
#define NANOVG_INCLUDED
#include <nanovg.h>
#define NANOVG_GL3_IMPLEMENTATION
#include <nanovg_gl.h>
#endif

// More #includes ...
#include <Game.h>


Game::Game(std::string Title, ScreenMode ScreenMode, int Width, int MSAASamples, bool VSync)
{
  // constructor here
}

void Game::Run(){
  // Initialise openGl and NanoVG, then into main game loop calling `Render();`
}

Render.cpp

//various #includes .. (STL GlaD, GLFW)

#ifndef NANOVG_INCLUDED
#define NANOVG_INCLUDED
#include <nanovg.h>
#define NANOVG_GL3_IMPLEMENTATION
#include <nanovg_gl.h>
#endif

// More #includes ...
#include <Game.h>

void Game::Render() {
  //Definition using Nanovg
}

Here are some other things that may be useful CMakeLists Available Here
Full Console output Available Here

What I have tried

• Putting the line #define NANOVG_GL3_IMPLEMENTATION in Game.h
• Putting the Nanovg includes AND the #define ... in Game.h
• tried changing the location WHERE Game.h and the nanovg libs are placed with #includes ... (causes unknown type errors)

Many thanks in advance for the help with this issue