Change password for iCloud keychain / prevent it from being unlocked with computer password
I’m afraid the cloud keychain is the only one you can not lock your account out of so you'll likely fail to do what you ask. 

All other keychains are trivial to choose an different password - even the log in keychain is easy since you can change your log in password with the passwd command line tool. Then, each time you log in to your Mac - the keychain password will be what it was before you changed the log in password and have to enter the second password.

Most people hate that situation, but you could run that way intentionally if that suits you.

The iCloud Keychain is tied to secure tokens so that you can have different passwords on different devices and I believe it uses your iCloud password to generate the unlock tokens. If so, you’ll have to disable iCloud Keychain syncing in all likelihood to lock / change it via passwords.