Dog Repeller - That Works!

[Kasper]

How about a deer repeller?  Our garden has been savaged this year by deer!  I've been thinking of a vary sensitive PIR motion sensor connected to a motor that clangs a bell for a few seconds.  I don't want to drive the neighbors crazy, but I want the deer to stay out of the garden.  We have a 3 foot high fence but they just laugh at that!
All suggestions welcome.
Jon

I've had a couple neighbors with 'ultra sonic' deer repellers in the past.  Fortunately they weren't close enough to hear from home but I always hated them when I went for a walk.  One stopped working after a while, I figured the battery died and they didn't realize.

[Haenk]

I've had a couple neighbors with 'ultra sonic' deer repellers in the past.  Fortunately they weren't close enough to hear from home but I always hated them when I went for a walk.  One stopped working after a while, I figured the battery died and they didn't realize.

Our neighbour hates cats, and we happen to have one - as do most of the other neighbours. So he installed an ultra sonic device, PIR activated.
Luckily, my hearing degraded, but my 16yo is quite annoyed by it.
However, the cats do not care. Like at all. They learn fast that there is no danger involved, so they ignore it.
So I highly doubt this will work for dogs either.

[n4te]

For places that have aggressive wild dogs (eg Romania) an air horn might help. It's something in a can under pressure and a horn that makes a terrible, loud honking sound.

For a yard, the motion/sprinklers and electric fence ideas seem good.