My DM has given me a magic item that is great, and I passed it by the people on this site to see what they'd say about it. The only issue they brought up was if I lost it, and I'm at a loss.
What can I do to, ideally, permanently keep my magic item from being stolen, lost, or destroyed?
Obviously, if the DM doesn't want me to have it anymore, I'll just give it up, but I'd prefer that there wouldn't be any small-time hijinks until then.
Before you get too worked up about the risks with the item, first talk with your DM and table about whether or not this is something to worry about.
As you stated, this started with Yakk's answer that said:
The only risk is ... what if you lose the drum?
Now, Yakk isn't wrong, but that's really the case for every magic item/special item/meaningful item/mcguffin that's out there. And the only time that's really a concern is if the DM is of the type that takes things away - or if you made a paranoid character that has this level of security as part of their persona.
The other answers here will absolutely give you good solutions for how to keep it more safely. There may even be answers that offer character builds like a Pact of Blade Warlock to help resolve the problem.
But the bigger problem is in whether or not this is a recurring issue at a table. I was once at a table where it was, and I can tell you that as a player, it's no fun. It's a good tool in the toolkit to create a specific feeling for an encounter, but it's too easy to be overused and just leave your players feeling frustrated that they can't even do their fun stuff when they finally get a chance to play.
Which also leads to the issue that if this is a DM driven decision, then that DM will find a way around your solution as well. If their goal is stripping of items, then items will be stripped.
Magic mouth is a low-level option that is accessible to you as a bard from third character level (you stated Bard is your class in your other question about the item). It allows you to permanently enchant the item until dispelled, and only costs you 25 gp. It triggers upon circumstances you choose:
The triggering circumstance can be as general or as detailed as you like, though it must be based on visual or audible conditions that occur within 30 feet of the object.
and
When that circumstance occurs, a magical mouth appears on the object and recites the message in your voice and at the same volume you spoke
You could for example embed a message of you loudly saying: "Alarm! Thieves! Robbery!" that triggers if the item is moved more than five feet away from you. The effect is even reusable whenever the trigger occurs. It will not protect against destruction, but is effective against the item being lost or stolen.
The chance of the item being destroyed are low as long as it is carried or worn by you. Most effects like fireball that could do that in earlier editions don't any more in 5th edition. Even if the item is subjected to damage, as a non-scroll or potion magic item it also likely benefits from Magic Item Resilience (p. 141, DMG), and has resistance. To make it virtually indestructible would require it to be an artifact or to have the "unbreakable" minor property (DMG, p. 143; thanks to @InternetHobo) to begin with. I'm not aware of ways to make an exsiting item permanently indestructible in 5e.
Drawmij's Instant Summons is an expensive option, but it's the best option you've got (assuming the item weighs 10 lbs. or less). At the cost of a 1000 GP sapphire, if the item is ever stolen in the future, you can crush the sapphire, and if the item is not currently being held or carried by another creature, it comes to you instantly, from anywhere (including another plane; arguably, this might allow you to summon it if it's in a Bag of Holding or the like, depending on how your DM defines "carried"). If it's being actively held or carried by another creature, you at least learn the identity of the creature who took it, and their rough location, which is the best you can do.
The spell is written as if only the caster can use the sapphire this way, so if you're not the caster, RAW you can't use this approach, but I don't see a big issue with the DM letting the caster give the sapphire and the name to another person, assuming you can't cast the spell yourself (it's a 6th level Wizard spell).
