OK lets say your in 4-8 foot of water. You find the perfect dept. Now reach down at water level pinch your line TIE a small loop. Now you have your distance marked so all you have to do is let that much line out after you re-bait. Works excellent. Your not casting so the loop won't hinder your operation. You can also mark the line with a perminate marker. The loop works suburb. Try it!! No more guessing and adjusting your presentation.
You can also take a soup can drill a hole @ the top of the can, pound a nail through the hole into the ice in your hole, lite a candle and this will help keep the water from freezing. Of course submerge the can in the water.