MarkV,
I think what you are talking about is marketed as "Spray Away." We have had great success using "Spray Aways" against deer in the Michigan woods for about three years now.
Amazon.com: Havahart Spray Away Motion Sprinkler - Protects 1000 Sq. Ft.: Home Improvement
The Spray Away needs a water hose and a 9V battery. Its electric eye senses movement (of deer, kids, anything), then opens a valve and sprays water randomly for several seconds. The pattern is varied enough that the deer don't seem to get used to it and are consistently spooked.
Others are right. The deer will keep probing for weak spots. I see occasional tracks in the garden, but they skeedaddle when the 'lectric eye sees 'em and blasts water around 'em.
By careful aiming, we've protected a 10,000 sq. ft. garden with four Spray Aways. You can chain 'em together one to another with hoses. You can mount 'em on the ground or with a hoseclamp to a metal fencepost.
They don't keep 'coons out of sweet corn. And I'm told they don't work if you forget to turn on the water at night or if you let your battery die (although our batteries typically last for our short summer)!
A little pricey, but I've gotten three good years out of 'em.
Joe
