What can I spray on my pigeon decoys to repel water droplets?
I have never really felt the need to try and waterproof decoys.
By and large, pigeons stop trying to feed if it is raining heavily, preferring to shelter in nearby trees until it stops.
When it does stop, and the birds start to move again, the decoys soon dry out.
Having said this, I have, on occasion, shaken droplets of water from dead birds set up as decoys, though I am not convinced it is necessary.