Welcome to a new concept for your very limited knowledge about Bitcoin: Accounts in HD wallets (No, not the old accounts system from Bitcoin Core). See: https://en.bitcoin.it/wiki/BIP_0032 or https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki#Specification_Wallet_structure.

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Hardware wallets have accounts trivially built in. If you accept deposits in m/0 for relative 1, and you use m/1 for your own money, then you will not be able to create a TX linking UTXOs from both accounts.