Maybe my fellow forumites can help me out here... I want to do an experiment, but I don't have the resources. Sharon, maybe you and your husband can help here, if you get a chance.
Here's the protocol:
Try kote-gaeshi, nikajo, or another of your favorite wrist locks under the following conditions:
1. Both locker and lockee on pavement.
2. Both locker and lockee on grass.
3. Locker on pavement, lockee on grass.
4. Locker on grass, lockee on pavement.
I have a theory, but I don't want to ruin the experiment by stating it. For the experiment to remain valid there shouldn't be much of an elevation difference between the pavement and grass. Anyone who's interested please give it a shot and report in, but try to be as objective as possible.
I will tell you the theory after the results come in, even if the results don't support it-- I've been wrong before.