Make a bunch of lyres that all look like the lyre, hide them in various obvious places, use Shrink Item on the lyre, wear it as jewellery.
PaO the lyre into a copper coin. Put an invisible arcane mark on it. Use Nystul's Aura Remover (tm) to get rid of the auras. Buy something. Whenever you need the lyre, use that spell that calls something with your mark on it back to you.
Design a bodyguard cohort. Have him bodyguard the lyre.
Design the toughest, nastiest, construct you can find. Put the lyre in it's chest cavity, removeable only by destruction of golem or craft [blah] check of [very high]. Put a trap in when golem is opened up without that check - > teleports lyre somewhere else.
Essentially you just want to make it so some uber-rogue can't steal it, and taking it would involve at some point fighting your entire army. Safes and things are not your friend, but multiple layers of defense are. Giant hard to move building with no openings + construct playing Lyre is actually pretty good. Problem is if you command it to stop someone could steal that ability and also do that, and then bam. You want some kind of active defense/mobile defense going on there. Don't forget to arcane mark the Lyre so you can Retrieve it if you need to. Also, I have wanted to play a good civilization/strategy/nationbuilding game using dnd for a very long time. Way better than a computer game with a real person in charge.