[leon_heller]

Many years ago a colleague of mine, knowing that I was an experimental psychologist, asked me how to prevent their cat jumping up on the ledge outside their bedroom window at night and waking them up, wanting to be let in, although it had a cat flap. I remembered that most cats find puffs of air in their faces highly aversive (it's been used for negative conditioning in some studies), so I suggested that he used an electrical puffer assembly from one of the photocopiers we made, controlled from a button by their bed, to deliver a puff of air to the cat's face via a tube with holes mounted along the window ledge. He installed it and after a few puffs over one night, the cat wouldn't go near the window ledge. The noise made by the puffer would have helped, as well.

Such a solution might be difficult in a garden, though.