How to use System::Threading::Interlocked::Increment on a static variable from C++/CLI?

I would like to keep a static counter in a garbage collected class and increment it using Interlocked::Increment. What's the C++/CLI syntax to do this?

I've been trying variations on the following, but no luck so far:

ref class Foo
{
   static __int64 _counter;

   __int64 Next()
   {
      return System::Threading::Interlocked::Increment( &_counter );
   }

};

From stackoverflow

• You need to use a tracking reference to your _int64 value, using the % tracking reference notation:

  ref class Bar
  {
      static __int64 _counter;
  
      __int64 Next()
      {
       __int64 %trackRefCounter = _counter;
       return System::Threading::Interlocked::Increment(trackRefCounter);
      }
  };