"bunch of people have access to it" +"I do not want anyone who can login as common to be able to login as secure as well" – If common can edit its own
.bashrc then maybe some person has cleverly injected a conditional script there and your password to secure has already been logged and is known to the attacker. If the shell is something else than bash, there may still be similar ways. Using an account that is "unsecure by design" to log in to a "secure" account is actually insecure, unless the "unsecure design" is carefully designed do disallow such attacks.