There isn't one solution that's safe for every situation. It is not possible.
Let's say you memorized your seed words... your brain can always go dumb and then boom you are poor.
Let's say you wrote them on a piece of paper. That piece of paper might get burned, might get lost... Your dog could eat it.
It's not only become dumb, when you get older, there's no guarantee your brain is always good as before since brain injury could happen to every people, just like this thread
Bitcoiners with Alzheimer's. How do you work it out?.I don't think dog will eat your paper lol, but most likely bugs e.g. booklice, termites etc will eat it. There's also a chance you the ink will be blurry or your writing isn't really clear, it might make you mistakenly missing for few words.
The best way is using stainless steel plate where it's immunable against fire, corrosion, etc. It will be good if you teach your kids or someone you love about Bitcoin and tell where you leave your seed phrase.