Requested WoW macro

I have a formal example of my macro .I am a goblin priest on Stormscale and my character name is Christosu . I have seen all sorts of varioation for the macro that I whant ,but they dont do what I need it to do . SO it is about Shackle Undead combined with Silence combined with a third spell ,any spell that can be casted it my target is not undead .I plan to use it in PVP .So this is what is going wrong . Example : The silence dosent share cooldown with my spels ,it's instant and I can cast it same time with another instant spel ,or a cast time spell .
/cast Silence
/cast Shackle Undead

this is what it dose so far : Alway on my target ,I dont need to focus ,or mouse over keep it simple : On undead it casts silene and Shackle undead .This works .
Then my macro is like that in 2 rows ,but I whant ,and I already added a third row
/cast Silence
/cast Shackle Undead
/cast Rocket Barrage(Racial) —- or any other spell

I whant to be posible to cast this macro on my target that is not undead ,I need it to detect if it's undead or not ,and then move on to the third spel and cast Roket barage ,or any other spel.
in the second row …. there must be set an conditon that I dont know because .Because if the target is not undead ,it just casts silence ,and then because it's not undead it sayes INVALID TARGET ,and stops ,it dosent move to the third reow . SO

/cast Silence
/cast Shackle Undead —— I need condition if the target is not undead to move on to ROketBr
/cast Rocket Barrage(Racial)