Make sure that the people who you are working for during normal hours don't try to make predatory claims on your side-project IP, to start with. Apply the minimum amount of violence necessary to ensure this, preferably zero.
Doing zero violence insures this. I think what he means by violence is violating company policy. If you violate it a bit by say working on your side project during work hours then you can not ensure that you won't have problems later.