do any of you guys use a gps as an aide for ice fishing? what kind would you recommend, i dont know anything about gps. i need it to do 3 things: 1. mark spots on the ice that i would want to return to. 2. make it easy for me to get to marked spots either from spots ive found on the ice or promising spots ive found on a map. 3. be rugged....waterproof would be nice. and withstand cold temps. any suggestions (pro or con) are very much appreciated!