This question already has an answer here:
When the Ethereum fork happened a few months ago, users were cautioned to protect against so called "replay attacks". A replay attack, as far as i understand it, is when a transaction occurs on one fork and an adversarial player submits the exact same transaction onto a second fork. A contrived example would be an XMR->BTC exchange that takes your XMR on one fork and then, secretly, replay that same transaction on the older fork.
This question is mostly theoretical rather than a pratical concern of mine. i imagine that Monero hard forks very rapidly reduce in value and so replay attacks are probably not worth much (you have to have a buyer, afterall) and after a few weeks the Mixin Transactions likely make an exact replay impossible.
But there is anything i need or can do to protect myself against a replay attack? Are replay attacks "features and not bugs" in the case of short one-to-three orphan blocks (a vendor could probably resubmit a transaction trapped in an orphan block if they notice it in an hour or so)?