Disable Re-targeting / Lock Target of a unit

[Bigabig]

Hey,
let me start with an example to illustrate my problem:

I build an arrow tower. My enemy wants to destroy my arrow tower with his knight. Therefore, he makes and Attack-Move-To Command to a position near my tower. The knight attacks the arrow tower. I want to defend the tower and order my sniper (that stands way behind the tower) to attack his knight. The knight will attack & kill my sniper, then again attack & kill the tower...

My problem here is that the knight decides to attack the sniper, even though he is currently attacking the tower and even though the sniper is far away.

A solution would be to either disable this re-targeting behavior, or to force the knight to lock-on this target.

Is there a way to do that?

I already tired setting the Stats - Priority value of all involved units to 4.
Also, I tried setting the Defense type of all involved units to Normal.

 

[DoomBlade]

Have you tried to force the knight attack the arrow tower with triggers?
I remember having a custom taunt that worked like that.