how to make spell which u cant dispel?

i wanna know is there any way to make some blizz spell unpurgeable - disable dispeling... per example bloodlust spell? or any other? or its only possible if its made in trigers...?

you could do something like

event
unit is target of ability
condition
targeted unit has buff (or w/e) = Test
Event
creat one dumy caster at position of unit casting ability
cast Test spell on target unit

u mean recasting thing... but how to be sure that it will have good duration?
set timer on 1st cast?

ya that would be easy nuff like you said just use a timer also make shure there isnt a casting animation on the dummycaster casting the spell or it would look kinda odd ;P

EDIT:

Also remember to set another trigger

on timer expires remove spell ;P