Grognard79
Villager
Shadowdark already has concentration. It's called "Spell Focus" (core rule book pg. 50). You have to roll every turn for a focus spell to see if you can maintain it. You also have to roll immediately if you are distracted; e.g. if you take damage.I'd add concentration. Maybe only for the light spell.
Also for the new permanence spell, I'd make it last for only as long as the caster lives. Maybe it could be a new thing like Concentration, call it Lifetime. Not sure of a name.