Improper grounding leads to little power at your fence, and is the most common problem in non- or mal-functioning fences.

Check the earthing

Testing the earthing.

To check the earthing you'll need one of these testers:  
Digital voltmeter Digital Voltmeter 075037
FaultFinder FaultFinder

Step 1:

Measure whether there is a current of more than 3000v on the fence wire, at least 100m away from the earthing system. 

Step 2:
Create a short circuit in the same position, so that there is less than 1000v on the fence. You can create a short circuit by putting iron posts against the wire. 

Step 3: 
Measure the current on the earthing system. If this is more than 300v fit more earthing rods and repeat the test.