Using the de-icer constantly can use a lot of energy, so it's better to only use it when needed. Keep an eye on your pond and only turn on the de-icer for a day or two when you see the hole in the ice closing. Alternatively, use a small heat gun or a pot of boiling water to make and maintain open a hole in the ice. Be sure to heat the area only up to the point where the ice has melted. Warming the water can put your fish at risk since they're unable to tolerate quick temperature changes.
A hole in the ice makes sure that your fish are getting oxygen, and harmful gases formed from decomposition have a place to escape, so you want to make sure that hole doesn't seal over if you're absent for a few days. In this case, it's probably a good idea to run the de-icer all the time while you're gone. If winter weather is predicted or power outages are possible in your area, it's probably a good idea to invest in a battery backup or have a neighbor check on your pond while you're away.
