The Fastest way I know of is, "Destroy Followers' skill that I demonstrated in the video above. Basically what you do is;

1- Assign the orc you want to kill as your bodyguard, teleport to any Haedir tower and call him while you're on top of it. Since Haedir towers are considered Safe Zones, nothing will bother you while you're there. (Maybe a nosy Drake will sometimes come to say Hi!, but that's about it)

2- Use 'Destroy Followers' ability as showcased in the video and any follower in the vicinity will have to bid farewell to their heads, which minimizes the chances of them returning back from the dead. Olog Hai's "Stitch" is one of those exceptions when a follower can come back even after decapitation.

Even though dominating and using "Shun" on the orc is the fastest way to get rid of your follower(Besides using above mentioned "Destroy Follower" ability), this does not kill him. If you want the orc replaced you would still need to go and hunt him, which spawns a bunch of grunts and other unfriendlies, making it much longer and harder than it could have been.

You could attack the summoned orc until he turns on you and since there won't be any other grunts to help him out, it should be a really one-sided 1v1 fight up there.

Note that, if the summoned follower is an Undead, he will NOT turn on you, since they're eternally loyal and are already dead. So you can just smack him to death, or grab him and shank him repeteadly, but in that case using "Destroy Follower" is an instant solution to your problem instead of smacking him for a straight minute.