How to move gameObjects around the point?

In my game I am trying to make enemies move in the circle around certain point. But when I use transform.RotateAround() their local rotation also changes. I want their heads always to be pointing straight up.
That is what I use for the rotation:

transform.RotateAround(point, Vector3.forward, 20*Time.deltaTime);

Thank you.

You can fix their rotation after every call to RotateAround. Something like:

var q = transform.rotation;
transform.RotateAround(point, Vector3.forward, 20*Time.deltaTime);
transform.rotation = q;

Alternately you can use a vector and just reposition your object:

#pragma strict

var point : Vector3;
var speed = 20.0;

private var v : Vector3;

function Start() {
	v = transform.position - point;
}

function Update() {
	v = Quaternion.AngleAxis(Time.deltaTime * speed, Vector3.forward) * v;
	transform.position = point + v;
}