I use the Lucky portable fishfinder for all of my canoe trips. For longer trips, you will need a portable solar charger as well. On the low-tech (no battery) side, you could mark off a rope at 10' increments that attaches to a rock or sand bag anchor. However, the anchor option doesn't help while trolling.
Good luck!
ejsiljen: "I have used a CUDA depth finder for the past 20 years, but they have finally wore out. Has anyone tried a Hawkeye Fishtrax and have any feedback?"