How to prevent Safari saved passwords being seen with Mac password?

If you want to avoid the default behaviour, which is a reasonable setting for a computer that allows multiple accounts, including guest accounts, you can do the following in Keychain Access:

1. Change the Keychain password
2. For each really sensitive item you have in there:
   1. Select a relevant item in Keychain Access
   2. Get information on the item with the Get Info menu
   3. Select the Access Control tab
   4. Mark the Ask for Keychain password checkbox

That should allow for the most sensitive passwords (or all of them, if you apply it to all of them) to require your password to be provided every time they are about to be used, and hence won't show in Safari's saved passwords unless that Keychain password is provided.

Another option is creating a new keychain, different from the login keychain, with a different passwords, and move the items from the login keychain. The system can find the needed items in that keychain, and you will need to provide that different password instead.

Of course, another option is using 1password.

Change the keychain password, and then lock the keychain when not using the Mac. Unless you want everyone to be able to login to your accounts. Then it's just that you need a change in policy, not in keychains.