If your senior programmer doesn't know much about systems and he has the root password, I suggest you use the command passwd to change the root password.

Then, set up sudo for that user so they have a list of defined commands they can execute as a super user.

else, I suggest that you alias the command su to something else that echos a warning to the user.

then run the su command as a different name. You NEVER want to re-engineer security around a user who should not have privileges in the first place. Root is not "the boss" he is god on that machine. He can instruct the machine to destroy itself (software wise). Cleaning up those messes will not be fun.