For one reason or another, you want to destroy your stamped or punched metal seed storage. Specifically because you want to dispose of it without someone finding it and being able to identify the words in your seed phrase.
But, people (including you) tend to store their seed on metal for a reason: to make it virtually indestructible.
Counter-intuitive, I know. You're stuck between metal and a hard place.
Fact is, destroying a seed stored on metal is quite impossible without industrial tooling that can either cut it up or melt it beyond recognition. Not many people have access to such tooling.
But don't fret, there is one thing you can do: make it extremely unlikely to be able to guess each word by obscuring each word..
Obscuring the Words
If you have hammer and stamped metal seed storage, you would stamp additional letters on top of the words.
If you have center punch style (like Blockplate), you would punch additional holes in each column for each letter.
But what letters do I mark?
BIP39 Mnemonic Wordlist Letter Frequency Analysis
We put together a BIP39 mnemonic wordlist letter frequency analysis: the most common letters up for each letter position in the BIP39 wordlist. You would mark or stamp the letters that most frequently show up in each letter position for each word to reduce the probability of being able to guess the entire word.
(For Blockplate, you would only need to worry about the first four letters)
It's up to you to choose how many letters you want utilize to obscure your words (obviously the more letters you utilize, the harder it is to guess).
Generating a New Seed Phrase
Although, if I had to recommend an absolute guaranteed way to prevent someone from guessing your seed (and any exposure for that matter), it would be to generate a brand new seed phrase and "transfer" your funds to it.
I understand. The fees, the hassle of sending your coins: it can be a major pain.
But, it honestly might be quicker than trying to obscure your seed. It definitely takes less physical effort to say the least.
Generating a new seed would be safer in the long run and you wouldn't have to worry about someone being able to guess your seed in the back of your mind. If it lets you sleep at night, it's worth the effort.