Backcourt Violation Technicality

[airpolgas]

I was taught this in my Basketball PE class more than 10 years ago by my school's basketball coach:

"In oder to establish yourself in the frontcourt, both your feet, and the ball, should cross the line."

He then proceeded to dribble the ball in the backcourt with both feet in the frontcourt, then stepped back in the backcourt. He said that was not a violation.

I showed the move yesterday to my buddies while waiting our turn in a pick-up game and they all cried violation.

Who's wrong? Who's right? Was I taught correctly by the coach, but the rule became outdated (remember, that was more than 10 years ago)?

Thank you.