Winterizing Pond - Heaters

After much research, I've decided to use solar bubble wrap pool cover
floated on the top of my pond and a titanium tube-style heater. The
pool cover will have a border of about an inch to allow gases to
escape. My questions a

1) How do you use one of these acquarium-type heaters? I would imagine
it would burn the pond liner if I just throw it in there. If I suspend
it, I would be concerned of it getting knocked loose. Do I need a
wire/mesh case to keep the fish from burning themselves?

2) I've read bio filters are useless below 50 degree. So I won't run
it. Is it better to remove it from the pond, or just leave it? I
anticipate the heater will keep my pond around 40. I don't intend on
"heating" it, just keeping it from freezing solid.



FYI: I am in zone 5, 500 gallons, 30" deep, 6 Koi