Yes, a pool blanket is next on my list if I need one. I was hoping to avoid using one since it will be a PITA to put it on and take it off every time the weather changes.duncan, have you considered a solar bubble heater/blanket? they use the sun to heat the water a bit and keep the heat from escaping. my dad has one on his pool and when you roll it off you can feel the heat. you might find one on craigslist for cheap.
about that heron: if the fake one doesn't work i've heard of people using mirrors facing up (spooks them), fake owls (some take batteries and have a motion sensor, they hoot and move their head) and if you want to spend a little more money, scarecrow sprinkler. good luck!
I have a dog that really hates birds, I think she is going to be spending more time outside this winter lol.