You don’t need a slingshot or a hawk. (Though, honestly, a fake owl statue is a classic for a reason.) Place it on a post near their favorite hangout. Move it every few days so they think it’s real.
How To Keep Pigeons Off Vegetable Garden at Troy Haynes blog
But plastic owls get boring fast. The smarter play is netting. Drape bird netting over your precious plants or garden beds. It’s cheap, invisible from a distance, and stops them from landing.
For ledges and flat surfaces, try “pigeon spikes.” They look a bit mean, but they’re just plastic or metal strips that make it impossible to perch. Think of it as a “No Loitering” sign for birds.