Motion detector...servo motor...BB gun...spotlight...siren...remote control....
....yes, you can solve this problem.... 
Throw in the ability to control the bb gun from a blackberry and I could have alot of fun "defending" the garden.
"honey why does all our vegetables have gun shot wounds? Dunno dear must be the birds."
The dog jumps over the gate.
Gates have some decorative metal work on top that makes them a good 6" taller than the rest of the fence. Don't think he can jump that.
