How do you find breaks surrounded by an electric dog barricade?
drag your dog around by its leash,
no just kidding, bid an electrician, there is a tool that can check it for you
This is done in the same path you find breaks in any wire.
Check out the lead itself. If it entails digging it up or removing it from a wall, this may be required. Use resistance measurements to isolate segments and move about from there.
There is no easy instrument.
Answers: I dont think an AM will respond to the frequence but you are correct if your using one of the wireless type fences. I believe you will involve an electric fence voltage indicator (usually in the 10,000 volt range) and attach it to the electrodes on the collar this mode you can see it lite up when you cross the good part and it wont lite where on earth its bad. You can buy aligator clips at Radio Shack (and maybe a tester too) to build the connections to the collars electrodes easier and more secure.
Also before you start amendment all the batteries and check the mobile connections.
Put on the collar and walk around. I don't see any other agency... Is this an underground fence? If above ground even a blade of grass will cause problems.