Managing Object Accounts Used Across Multiple Companies

Hi

I need some advice on the best way of managing Object Accounts across multiple companies. We have some accounts that are exclusively used by specific companies and would like to know the best way of keeping track of these so that if an account were accidentally added to a wrong company it would be easily detected. I was thinking of using  a category code for accounts that were specific to certain companies so that we can run a report to easily detect where accounts have been incorrectly copied to a company.

Is there a better way to achieve this or is there a way to prevent certain accounts from being copied to certain companies?