Hi Jeff,
You can place the safety on either end of the bar but preferably use the ring with the "borble" on the left hand front line.
By attaching it to the back lines the kite will death spiral pretty badly in strong winds and can twist the lines into a solid bunch if you are unlucky.

You can also attach the safety clip to the ring on the end of the chicken loop line where it clips back into the Quick Release Mechanism, This is good for handle passing or if your chicken loop comes undone you can retrieve the bar and not have to worry about spinning the bar and getting tangles. It will work sort of like a suicide leash but you can still cut away if necessary.
A better answer to tangles is to purchase the spinning thingy that the Halos come with and attach the spinning thingy to your spreader hook, end of issue and you can attach the safety to the front lines with no problem. Fool proof depower!

Better to stick with the front line, it works perfect just about everytime.
Good winds,