I've seen a thing on the interweb, it was about £50,
that you attach to your hose, and leave in the middle of the garden, and it has a movement sensor and sprays water in the direction of where ever it detects movement.
My garden would become a swamp.
( turb0t, Tue 16 Jun 2009, 19:02, archived)

They'd learn soon enough, though.

( Esme Weatherwax I swear on my tash it's daycent hash, Tue 16 Jun 2009, 19:05, archived)