Are magics like SAFE and SHEL cumulative?

I was fighting this boss in the Mithril Mines the other day, and I always thought his physical attacks were very strong.
So I thought: "hey, I'll just cast SAFE and BLNK on my chars for eternity; this will increase my defense with each use! :D"

However, I'm not sure this is correct: does each use increase my defense, or does it only work once?

Once. But they do wear off.

SAFE, SHEL, BRSK and BLNK can all be stacked several times, the number of times it stacks per casting depending on the level of the magic spell and the relevant statistic of the caster (in the case of SAFE, SHEL and BLNK Spirit, in the case of BRSK Intelligence). The level of the spell is how many times the spell will attempt to be "layered", whilst the relevant statistic of the character casting it determines the chance of that occuring, along with a built in accuracy.