LOCK for asp.net developer using vs 2010 and win xp?

I am hiring few extra trainees who will use their personal laptop at my office to work on .net projects.

I want to restrict the code/file access in their laptops with password. Like when they get in office …they will ask me to type password to start work and when they leave office with their laptop …i will ensure they “log off” so that cant access the code at their homes.

USB drives are not allowed for trainees & internet access is limited as well.

Note :In my country, laws makers are not that mature in these things …so have to take this type of measures!