Why would you do it randomly? When you have the rods, you are using your eyes to navigate the environment. If the dowsing rods are just a way to help key you into your own senses, like seeing depressions or slight differences in color, or feeling slight downhills while walking, then the control should be trying it without them.
If I clamed I had a pair of glasses that improved your driving, the control would not be driving blidfolded.
It's possible that you are biased towards dowsing and thus not a good control for the experiment. You want dowsing to work and thus try harder when dowsing than when not.
So the intentions are part of the dowsing process, and the science has not caught up with that yet.