I just came across an article, doing a google search, that specifically deals with the whole issue of uke tensing his wrist to prevent take down.
A guy by the name of Christ Tozer quoted 'O' Sensei and went on in about 4 more paragraphs to explain that how with little extra effort that you should still be able to take down someone tensing.
Some aspects of anatomy and muscles how they work were pointed out in 'proving' the theory...it seems 'sound' in idea, but as pointed out you have to have your movements co-ordinated.
This includes the timing of the movement of your hip to your hand...which at this time I still rely heavily on my hand to move hand into wrist lock.
I would post from the thread here, but Im not sure the rules about giving links to other message boards as well as how much is permitted in quotes - (i.e. whole thing as long as name is included, etc.)
It really goes straight to the heart of the issue, and again brings up an aspect/technique that a user here pointed out...which I was unfamilar with.
Particularly the question was posed if I used my thumb or rolled with my fingers.
I usually roll with the fingers, but apparently 'O' Sensei was recommending to not grab the wrist, per say, but to grab with your thumb under the pinky and ring finger to get control over the wrist.
The movement would be like a cutting motion down - and as you turn your right and would turn the hand pushing down as well...with ukes hand and your hands lining up at your center.
Now all I need to do is get this guy to train with me more...he is kind of stand offish and trains selectively...again, I suppose it has to do with the language bit...who knows.
- The info came from an older article from 2000, Chris Tozer - again, Im not familiar with the policy of reposting articles, etc. thats why I didnt.