This is something I've been wondering/working on as well. I've tried alot of various knot/loop combinations with snare wire. On using the lark's head, maybe I'm doing somthing wrong but in wire it seems the wire kinks before the lark's head bites in so i end up with a loop that still runs.
What I've found that works reasonably well and doesn't use much more of the precious wire than a regular loop, is to add a small pinch in the running loop. I try to slightly overlap the pinch so it doesn't affect(jam) the sliding of the snare. It rides freely then with more pull the wire pops into the pinch to 'lock' the snare. I've been doing my tests with Mil. tripwire (the yellow and green spooled stuff), so YMMV.
I'm pretty proud of this innovation as it seems to work pretty well. Here's a pic:
As for the Wiseman book reference, It looks like they were refering to the Honda knot in the campcraft section (pg.168). I have the original "Survive Safely Anywhere" edition, so the page number may be different. Also, if you look at the diagram of the Prusik knot (pg.171) the first diagram is a Lark's head.
Dave
PS Let's call it the Dave Slide-lock <img src="images/graemlins/grin.gif" alt="" />