A fence will work but only if it's properly set up. If the ground is very dry, it might not because the bear won't get shocked. Also, the most important part of an electric fence is the ground. If it's dry, you might have to drive the ground rod in a hole and keep it filled with water until the soil is thoroughly soaked.
One article I read said that once a bear hits one, it learns fast and won't be back. So, they baited the bears with bacon smeared on one area of the fence. Then they dumped water on the ground all around the bait to make sure the bear was well grounded for the maximum affect.
