It knows rock slide but is there any other better rock type move I should teach it?
Actually, no, because Rock Slide is the best Rock-type move it gets.
It depends what you are using Excadrill for.
if he is an all out attack Pokemon and your not worried if he faints then I recommend stone edge. if you teach exadrill hone claws it improves its accuracy and attack making the 80 accuracy of stone edge not a problem.
but if he is more of a sweeping Pokemon used to take down weakened enemies teach it rockslide because of its improved 90 accuracy C: