Help with Orb of Lightning/Orb of Slow

[Allen Walker 22]

I need help with Orb of Lightning/Orb of Slow (the trick of making a active spell into passive spell), I did it with correct cooldowns etc. but the thing is, when my hero is dealing with many enemy units, let say 3 footman if the passive spell activates then my hero will change target, is there anything that can stop this? thank you

 

[venger07]

dealing with many enemy units? does that mean that your hero has cleaving ability?
change target to where?