The funny thing with electric fence's is that everyone expects it keep going for... 4 years down the line, no service, no checks.. but its expected to protect possibly your life! Now that rains are here, home maintenance is a must!
Do yourself a favour and go around a clear all vegetation as far back as you can as this really saps the energy once the rains come - even to the point it renders it useless.
Minor arcing when its raining, not to serious or to worry about. Large arcing, loud and big visible spark you might want to attend to.
Check that the earth spikes are still connected - the mower, dogs, kids, rust etc often damage the ground spike cables and with no ground spikes, you basically have a half effective electric fence!
If you can, when theres lightning, unplug it for a while - same as you would do for your TV (which by the way doesn't do to much for your life but still gets looked after more!). Battery should keep you going a few hours. (dependent on types)
Look after it...it will look after you!