how to get transform.RotateAround to orbit, not spin

So i'm trying to simply make an object that circles around a center point in a tower defense game, however no matter what i put as the center point, it just ignores it and spins on the center of it's own axis which obviously isn't what i'm looking for. what am i missing to adjust it so it works properly?

the line of code in mention is as follows:

transform.RotateAround (gundad.gameObject.transform.position, Vector3.forward, 1f);