Thus, while I was gone, the dogs escaped time and time again as they were let out. Janelle and Trevor worked a bit on the reducing the size of the snow piles, but they had layers of compacted ice, and the foot or so reduction was not enough to dissuade the dogs from jumping. It wasn't until the day Connor and I returned that Janelle, out of concern that our wandering dogs would get injured by a car or moose, bought a short dog chain. It stopped the excursions, but added a level of frustration for both us and the dogs.
Today, I waited until the air had warmed and the rain had passed before spending over an hour outside, trying to create a ditch at the three places where the snow was high enough for the dogs to jump the fence. In each of the places, I dug down about three feet (or more) from the top of the fence, and cleared a space about three feet away from the fence. I used the gravel shovel I bought last summer as the snow shovels didn't have the strength to push through the ice layers.
Once I finished, I decided to test the moat that I placed on the inside of the fence. I let both dogs out together. Immediately, they ran along the snow ridge like they were going to jump the fence, but they both skidded to a stop when they saw the trench. After some investigation at the other sites, they decided to just do their business and ask to come back in.
Thankfully, it seems that they don't want to risk the longer jump. I certainly hope that this solved the problem. My arms are too sore at the moment to consider widening the moat even more.