Thanks man thats pretty good idea.
Not a problem.
In fact I was just trouble shooting this on Saturday, and found a couple of solutions myself. One is to attack the thumb. That seems to get some pretty consistent weakening of the clinched hand.
Yes, attacking the thumb is a good strategy, however it won't be available against, say, a punching attack. If they're just holding their fist out, fine.
There are things I could mention here (oya goroshi, for instance), but really unless you have a teacher who really knows these things they are a little difficult to properly get across here. And there best understood by feeling them being applied!
Two there is a pressure point on the upper forearm to grab or strike if the person happens to be sensitive there.
Within the Ninjutsu-related systems that point is often refered to as Nagare, and has the effect of opening up the hand. It is most often used against a weapon, within the muto dori techniques (unarmed defences against a sword). Again, good, but to really know how to apply this, a teacher should show you. Being slightly off in targeting or angle can make a huge difference.
I have to say MJS is really right though the amount of trouble shooting I have put into this just to make this technique as effective as I was led to believe it was is ridiculous.
Well, if it requires that amount of "trouble shooting", then that tells me that you haven't been exposed to the proper application as of yet. That's not an attack on your teachers, but if such techniques are not a common part of your system (from memory, they're not, are they?), then I think that's understandable. As with any technique, the application is the important thing, and simply taking something from outside of your systems teachings because someone else can make it work often misses a large number of important details, making it harder and harder for you to apply these new techniques.
And even now its still not the fifty million dollar technique they sell it as. I cannot figure out why they based an entire style of hapkido on these.
There is no such thing as a "$50 million dollar" technique. Each technique has an application in which it is ideal, and worth more than any other, and each technique has situations where it is less than useless. The thing is to recognise which is which.
As to why Hapkido based an entire system on these techniques, well that is because it is a perfect expression of Hapkido's philosophy. Hapkido is believed by most to have come from Daito Ryu Aikijutsu, same as Aikido, and as such it is based on grappling methods as many Japanese systems are. That is because it is a perfect match for the requirements, whereas striking and kicking is less effective (culturally and historically speaking).
So in short, although I don't agree that Hapkido bases their entire system on wrist locks, the reason they have a prominence is that it is Hapkido. And if you study Hapkido, you will be shown correct applications, and they will work. But the setting needs to be correct first. Hints online can only take you so far, really.
This thread has kind of run its course, but I think a discussion on joint locks as a whole would be rather interesting as well as a productive topic that most everyone could enjoy.