My two dogs go to my back gate, and just raise a fuss when a dog walks by on
the outside of the gate. They cannot see through the gate, except for a
couple of small spaces.

I want to set up a horn with an electric eye, so that when they go close to
the gate, it will sound. This will only come on if they go really close to
the gate, so it won't get them if they just stand back and bark.

My Lab got a cut by her eye, and I am sure that it is from where the small
spaces are, and she was trying to stick her head through.

Can you steer me to what I need? Would I just go to Radio Shack and talk to
the nerds there? How much do you think this will cost?

Steve