Let 2 SCH shields stack with diminishing returns

[Mhaeric]

is this true? never played whm at 50, but if regen stacks with other regen, then it doenst make sense for 2 shields to not stack

They definitely do not stack. If you cast a spell that grants the Galvanize effect (i.e. the shield) on someone who already has a Galvanize effect, then one of two things will happen:

1. If your new Galvanize effect is larger than the current remaining Galvanize effect, then the old one is overwritten and they receive the full effect of your new one. You can see this by noting that both before and after your cast there is only one green Galvanize icon on the target.
2. If the current remaining Galvanize effect is larger than your new Galvanize effect, then you get a flying text message on your target stating, "Your Galvanize has no effect!"

As for Regen, it's easy to tell they stack, because you can see multiple icons on the target. One for each regen effect on them. Notably, Regen and Medica II also stack both with themselves and eachother. So if you have 3 WHM in the party you can have 3 regens and 3 Medica II regens running on a single target at the same time.