Don't use the guild chest to store valuables. Use it to pass on stuff that you are already accepting that you will get ZERO for it. Basically, treat it like a recycle bin. As it stands right now, the regular guild chest has no access restrictions.
If you want a cache to store valuables in, then get the officer's chest, and don't promote everyone to officer.
Also, be a little more stringent on who you recruit. If you're going to pick up just about anyone with no prior play experience with the guild, then don't have a guild chest if you want to keep good items in it.
All this common sense is making my brain hurt!!!!!