Last year people asked the question on how you keep your hole from freezing over. Someone mentioned a device that if I recall correctly sounded something like the Spitter which is described below.
A couple days ago I was reading the first Hooked on Ice Fishing book by Tom Gruenwald and found this.
Quote:
Keeping your holes open
Once set up and fishing, you’ll be faced with the challenge of keeping each hole clear of ice and slush. If you’re “on fish” and not moving much, drill a second hole beside the actual fishing hole, chip out a channel between the two holes with a chisel, and place a coffee can full of hot charcoal briquettes into the false hole. Warm water will circulate into the fishing hole to prevent ice up. You can also use the charcoal bucket to warm your hands, as well melt ice from line guides, auger blades and scoop. After dark, the glowing coals can provide enough light for unhooking fish and baiting.
Water spitters are another way to keep holes open. A spitter can is constructed using a coffee can and a length of copper tubing. Bend the copper tubing into a coil, place the coil inside the coffee can, drill a hole for the intake at the base, and seal with solder.
Next, form a spout at the top, add sand to the bottom of the can, pile charcoal into the coil and place it in a shallow hole drilled next to the hole you’re fishing. Finally, chip a small channel between the two holes, and with the spout positioned over your open hole, light the charcoal. As the can and copper tubing heats, the water around the can will heat slightly and spill into the adjacent hole. The tubing will draw in cold water, warm it, and “spit” it back into your fishing hole, keeping it from freezing in your absence.
Commercially made items are also available:
*HT offers the Thermal Hole Cover, a flexible three-fourths inch foam pad that works with any tip-up, and the Ice Guard, a plastic cover that adapts to any tip up, including wind-tip-ups.
*Northeast Products offers the Ice Hole Insulator, similar in design to HT’s hole cover.
*Other interesting inventions, including the Hole Heater, can be placed in the hole or on the hole cover (with the line run through) to eliminate line freeze-up.
is grass. 
