You can stop anyone from getting to your software by using the following admin tool:
SITE SETUP > GENERAL SETTINGS > SITE ON/OFF
You can find about the site on/off feature here in the support wiki
While that's good you and your developers may still need access while you work on it. You can allow that by inserting you and your developers IP addresses within the following admin tool feature:
ADMIN TOOLS & SETTINGS > SECURITY SETTINGS > GENERAL SECURITY SETTINGS > Allowed IPs When Site Disabled
You can find more about allowed ips feature here in the support wiki.
This type of setup can also be used for testing or development installations of the software outside of your live installation.