You could add Magic Immune so it couldn't be targeted by spells.
Yup.Yup, just use that
yes, Magic Immune will immune the spell. But you channeling spell is still possible stopped by some passive skill such as bash, and ensnare.
you can try alternative method such as shorten the duration, use dummy to cast and teamwork!!! ask someone be the bait so you will have sifficient time to cast the spell.
LoL! just make a dummy to cast this spell. and then put a unit closer to this dummy and play it Spell Animation, and now, if the Bash "stun" him, the spell will not stop, cause it's a dummy who is casting it...