We have a 8 foot wooden fence around the entire backyard with locked gates. No one from the outside can get in without doing some serious climbing. In our area you can't get a permit to build a pool without a fence being in place.
I had a custom safety cover going on it in a week. I was doing so to keep my children & dogs safe, plus keep the leafs out.
I would have tried to recesitate the dog, but by the time I got to her, she had been in there for a good while.