Thom Hogan's D800 book, pg 431 says 'trap focus' no longer works on this camera.
So ... Russ may have a point.
You can also, with AF-C and AF-On, prefocus at a point all day long, pick up a target that moves under the focus point and fire - you have to push the shutter release now. But this works rather well. The new AF system is so fast, I prefer AF-C, Release priority unless I'm really doing subjects that are not (supposed) to move - then I may use AF-S.
I'm not doing macro yet, Dan so don't know about your challenges.