I've been trying out back button focusing (BBF) for a couple months now and appreciate the advantages. It's particularly handy for stationary objects (which few of mine are!). It's placement for my smaller hands can sometimes put my wrists at wonky angles if I'm shooting from down on the ground, but I can certainly go back to shutter focus lock for those times.
However, I find I'm missing a lot of shots of moving targets trying to re-focus. I'm not sure what I need to do to disengage the focus before I re-engage it. Pressing the AF-On button again is ineffective. It seems like I need to depress the shutter button halfway to be able to reset AF-On, but can't find anything in the reference manual or the Nikon site that tells. With busy moving subjects, the half-press to the shutter AND pressing the AF-On button is fiddly. I also get a frustratingly large number of protected files, although did discover that in ViewNX-i, I can select all and unprotect the whole group.
I'm hoping someone here will be able to tell me more clearly how to use BBF, since the online info is pretty scant.