Point rods forward, marginally downwards and marginally converging.
(Mounting them on a bike or the roof of a 4x4 is optional).
Go forward and when a particular point is reached, accelerate marginally. Rods will cross.
Marginally decelerate, rods will uncross.
Turn round. Repeat.
When rods cross again say Aaa-haa!
(Variations include starting with the rods marginally diverging, whereupon they’ll fly apart at the relevant moment or mounting them on a dog’s back and shouting “walkies!” at the crucial moment.)
I’ve done (some) of the above. ;) I’m NOT saying dowsing doesn’t exist and is all faked but making the point that rods can appear to have an amazing and confusing life of their own and to be reacting to an unknown force when in fact they may be actually obeying a subtle combination of good old gravity and Newton’s laws with absolute obedience.
Trouble is the above "marginal" stuff can be applied by we charlatons without observers being able to see, so real and fake performances appear indistinguishable. That's why scientific observation and testing is king IMO.