well if you are fishing in a good spot , you want to to come back to it in the moring to this hot spot just to find it froze over again, you could do like i do.
I take a can of air like you use on your p.c.,and a balloon that will blow up bigger then your hole.
blow it up and stuff it in the hole, then cover it up with a little snow so it does't stand out for everyone else.
try it , you mite be happy you did.
vern