Very Good Point. Take your master that you get from having your locks changed, to a locksmith and ask them to make as many copies as you need of "Do Not Duplicate" keys. They actually have that stamped on them and no legal locksmith will duplicate them. Then lock your master up in a safe place (if 2 masters, then separate them and have one off the property) and never use it in a lock only use the Do Not Duplicate keys. That way your master never has the chance to fall into restricted hands AND it doesn't have daily wear and tear so when copies are made, they are copies from a sharp, new master.
I do this for the church I work at. I used to have everyone making copies for the front door and then we got robbed and I re-keyed. Now, if they want a copy they HAVE to come to me. And I have a list of every key made with its owner.