Perimeter circuit needed

[mrbearuk]

I need a circuit to let me know if my dog leaves the perimeter of my garden.
My Labrador keeps trying to escape from my garden, no mater what I do he finds a way out sooner or later.
I need some kind of alarm that sounds when he goes past a certain point.

  Any ideas or schematics will be greatly appreciated.

[circuitous]

Okay, I'll need to start with lots of questions.

Can you provide some details on what you're looking for, or the environment?
Is it a big yard?
How far from the house to the desired warning perimeter?
Is it an apartment/flat, are there lots of radio/line-of-sight obstructions?

What sort of solution are you looking for?
Can it be a photo beam, etc?
Are you thinking of a wireless (radio) type solution?

I recall some GPS based solutions like this: http://www.pettracker.com/pet-gps
If it's short range, then you might be able to build a bluetooth device like this http://www.pettracker.com/pet-gps

[SeanB]

Most common is a buried wire with RF in it at around 49MHz ( ISM band that is license exempt around the world) and with a collar on the dog that trains it with a warning beep then a shock if it goes near the boundary. It will soon learn to associate the beep with the shock and the beep with the boundary of the property.

[circuitous]

Most common is a buried wire with RF

Yes, that's very common in the US, but I think the OP was looking for something to tell him if the dog strayed.
I think this thread will end, as the OP posted in another forum that echoed our suggestions.