To make sure a function started by a call_out() is wrapped inside such
an rlimits construct, you would have to redefine call_out() in your
auto-object, like this:

    static int
    call_out(string func, int delay, mixed args...)
    {
        return ::call_out("_F_call_out", delay, func, args);
    }

    nomask void
    _F_call_out(string func, mixed *args)
    {
        if (previous_program()) {
	    rlimits (MAX_STACK; MAX_TICKS) {
		call_other(this_object(), func, args...);
	    }
        }
    }

The 'if (previous_program()) {' condition is to make sure the function
cannot be abused by calling it directly, this way it will only call
the given function with the parameters if it's the start of a thread.

If you're thinking of making _F_call_out() a static function, think
again, because that would make it an 'efun' since it's in the auto-
object, and then you cannot call it from a call_out(). :-)