BrickUnderground

Advice, please. Pigeons have decided to move in under a window air conditioner that extends out over a ledge (thus, providing a lovely habitat). We got rid of the nest, but we think these squatters will return. We live in a preservation district and are not able to put in netting around the air conditioner. We may be able to use the spikes, but I worry about them falling on someone - the surface below is masonry and its not easy to screw the wood base into them, plus the corner is quite windy so they can't just sit there.  Any suggestions? Someone has told me to crumple up alluminum foil and put it on the bottom of the AC sleeve.