George S. Ledyard
Students need to have permission to allow their technique to be what it "wants to be" rather than training themselves to force their partners into some predetermined form demonstrated by the Sensei. Otherwise you are simply training them to force their techniques and killing their sensitivity. Very bad martial arts.
Ah this guy has always been my ideal Sensei :-)
And he is not disjointed imho: he is intellectually rich. This is why posts where George intervenes normally branch out in many directions.
However to put my two worthless and rough cents into the original question: when uke resists openly, what to do?
There are much more competent answers than mine.
However, right or wrong: personally, I brazenly wait.
I just keep my hands on uke's arm in the position I was attempting the technique, and to his usually evident bewilderment, I just stay with my hands on him exerting no force whatever and I just wait.
Some ukes look at me as if wondering: well, do something.
I won't. I wait for them to do something.
Yet if he waits for too long, I can suddenly produce an arm lock, and wait in that position.
Sooner or later he has to move. As soon as he moves I follow his movement and see whether a technique flows out of it to unbalance him.
When he moves I follow his direction adding a bit of my own force and if he loses balance, it is normally possible to place a convenient technique. You don't need a big repertoire - certainly I haven't.
True, most dojos won't let you practice this way. But, then, they also shouldn't allow rigid ukes too. But, then...
ps i am a guy who fell several times on the mat (and on the ground) toghether with Ukes, in a very unstylish fashion with my legs flailing in the air, who attempts occasionally to force a technique (bad habits never die), and whose techiniques utterly fail once out of three times - on top of that, as a tori I lost balance myself slipped and fell twice face down doing a tenkan + kotegaeshi go figure: so, by all accounts discard my approach.