You should protect your Apple ID with two-factor authentication. When you log in using your Apple ID you will be required to verify it with a code sent to one of your trusted devices. It doesn't take much extra time once you have set it up and understand how it works.
Log in to https://appleid.apple.com/, scroll down to the Security section and tap the Edit link to the right. Activate two-factor authentication and follow the instructions.
This will likely keep your Apple ID safe from everyone that isn't you.