As a Key Account Holder of the CRM you can request that tag based security is set up for any other users of the CRM.
This tag based security works by restricting access for users to only be able to see the contacts which have their name tag applied.
For instance, if you have a colleague called Tom then we can set up a tag called 'tom' which means that when Tom is logged into his CRM account he will only be able to see contacts that have his tag name 'tom' applied to them and no other contacts.
Please see the screenshot below to demonstrate this:
In addition to this we can also go one step further by restricting a users ability to edit tags - therefore they are not able to remove or change tags once they have been applied by the Key Account Holder.