How to tell what clickies and procs stack or not?

[Tobius]

I have Lesser Shielding from (https://wiki.project1999.com/Cobalt_Vambraces)
I have Spirit Armor from (https://wiki.project1999.com/Shieldstorm)

I just got on my alt to deliver to my main: Turtle Skin (https://wiki.project1999.com/Lodizal_Shell_Boots)

I want to buy:
Guard (https://wiki.project1999.com/Guardians_Mace)

Which of these stack? and what is the rule for telling this?