My friends and I tested this a bit a long ways back. When we created our own FC as the leader I simply only gave myself the ability to withdraw gil. Only me and 2 of my Executors can promote or demote and I trust them. Even if they did try to screw the FC over they could only take items from the chest, and we don't really keep high dollar items in there so we would be out of a few million at most. our 24+mil would be able to still fund events, raids, and other things. NOTE: Also make it to where only trusted members can mess with airships too. Those things get to the point to where their parts are expensive.