Theoretical hard fork - how to separate txs

[slothbag]

Lets say for whatever reason (deliberate or accidental) Bitcoin hardforks into two chains.. I have 10 bitcoins in my wallet, on chain 1 I would like to send those 10 bitcoins to address 12345 and on chain 2 I would like to send those same 10 bitcoins to address 19876..

Assuming both chains have nodes still relaying txs amongst both chains, how do I prevent the first tx from being applied to the 2nd chain accidentally? 

Is there a way to specify to only include this tx if block x hash = <some known hash>?

Any other way to keep the tx on one chain and not the other?

[1715186747]

1715186747

[1715186747]

1715186747

[1715186747]

1715186747

[Foxpup]

Is there a way to specify to only include this tx if block x hash = <some known hash>?

Yes. Use coins mined in that block as one of the inputs.

Any other way to keep the tx on one chain and not the other?

Make double-spend attempts to yourself, sending to a different address on each chain. Since both addresses belong to you, you don't lose anything (except transaction fees) if it fails, and after you eventually succeed, coins from each address can only be spent on the corresponding chain.

Alternatively, if different consensus rules make certain types of transactions valid on one fork but not the other, just create such a transaction.

[slothbag]

Thanks Foxpup, so..

* Use freshly minted coins (hard to get significant quantity from miners)
* Send coins to different accounts you own on each chain (trial and error, could take a few attempts)
* Try trigger different consensus rules (not always possible depending on fork reason)
* Try find a miner who can directly accept new tx (no relay) and place in one chain only. (not many powerful miners to choose from, requires effort from them to build)

Not really any great solutions.. probably the double spend until you have coins in separate accounts sounds best.