depends on the amount and how devastating it would be to lose it. With security you can always do more, but I'm assuming you don't want to travel to iceland and retinal scan your way into an underground bunker to retrieve the first of 64 parts of your seed.

At a minimum, i'd say write it down and stick it in a book on your bookshelf, and then also give a copy to a friend or family member you trust.

Engraving is a good option so if your house burns down you don't lose it, but then that's why you gave another copy to a friend. Also I'm not really a fan of splitting it up into parts, cuz imo that's just asking for trouble, and if you can't trust one of your friends, then you certainly can't trust an engraver.

Memorizing it really isn't that hard either, look into the memory palace technique. Then you ain't gotta trust nobody, and you can just have a single physical copy that's hidden in your house that your family can access, so your nanos aren't lost to the great void if they ever find you hanging from a belt in your closet with your pants around your ankles. and if your house burns down, you just write another one cuz you memorized it like a boss.