What programming languages are using ? What operating system ?

If you are on windows platform , you can enforce security so the devices and operating system. If you are using Microsoft compatible programming languages, you can use TFS as a source control and ticketing system. You can also use token based systems / cisco vpns and enforce security policies so that users can only use the internal servers / network to commit the code. ( Your IT Department security consultant can help with that ) .

If platform level security can't be guaranteed, you can still use distributed source controls, like GIT or SVN. Software management systems, like Jira or Versionone, can be used for the ticketing, and you can use smart commits for every commit, to help link code on feature basis . That also can be a base for a future plan for implenting TDD and continuous integration .

Finally, your team should be singing an NDA and make sure you work with people with work ethics. Motivate your team to be your asset and grow with you. This is your 100% guarantee.

Let me know if you need more help. .

Good Luck!