static variables with scheme objects

[sig]

I'm writing an extension module to guile in C and I would like
to be able to have a global static variable in C which holds a
scheme object. Something like:

static SCM global_mutex;

void init() {
  global_mutex = scm_make_mutex();
}

but it seems like doing this be dangerous as the garbage
collector would try to reclaim the object as its not an
immediate and the only reference is this global variable so
walking the stack wouldn't find it.

I thought about doing something like

void init() {
  scm_c_define("global-mutex", scm_make_mutex());
}

but this has the problem of not being accessable from other top
level environments. Does anyone have some advice on how to get
around this?

cya
.sig