If the real goal is having decent DO levels at all depths then just measuring the temperatures at various depths may be a valid way to determine if complete turnover has occurred based on this post from Bill Cody a few months ago.
It's a long read but worth it if you haven't already seen it.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=30739#Post30739
