Parenting binary effect on/off from a other layer

I just can't get it to work. But then why display the Spiral/Rope next to it.... if you can't link it?

It's an age-old bug/ design flaw that goes back to the earliest versions of AE when it was assumed that the complex dependencies such as they exist today would never even come to bear or be a problem. It simply iterates through all properties and adds the controls, but since there is no internal blacklist/ whitelist system or a way of tagging specific properties it doesn't know which ones to leave out.

Mylenium

This is a question I've asked before and unfortunately the answer is that it's not possible. The pick whips will write an expression when you drag them to a property, but you can only write expressions on keyframeable properties. The fact that there's a property pick whip next to non-keyframable icons is the real issue here and I've been told that it's not as easy as you might think to simply remove those pick whips from non-keyframable properties. You can file a feature request (or bug report) at UserVoice here: https://adobe-video.uservoice.com/forums/911311-after-effects