R. Haruo Hori wrote:
One of the first things we're taught in randori is how to change techniques if your opponent resists. Gyakugameate doesn't work? Change to kote gaeshi. Uke stops that as well? Transition to shomenate (and so on). It's all about getting a really good kazushi, if uke is resisting with force, that force is going in some direction - use it to your advantage.
Now I remeber Bill Witt Shihan's words: "No matter how good you are, sometimes technique does not work, then try something else".