RobC,
Here is the set up for my fishfinder...
This is the waterproof box with silicone in the corner. I used a 4 pin trailer connection that I spliced in and heat shrunk to keep out the water.
This is the open box pic, the wires have been siliconed in and the blue blocks are there to prevent the battery from jumping around in transit. I spliced in the pos. and neg. connectors into the other end.
This is a good view of the entire setup - the head unit and the battery pack.
This is to make evident that I permanently fixed the base to the cutting board. I also spliced in the 4 pin connector.
Only the head unit gets moved when I switch from soft water to ice fishing. I picked up an extra base and wire set to not have to move everything around when the season changes.
The only thing I would change at this point is to use a different type of connector; the wire is starting to break off at the connector. When it lets go, I will pick up a better (softer) connector that isn't so difficult to connect and disconnect.
As for leashes, I use one on my paddle tied to me and on my rod tied to the boat. I don't bother with an extra paddle - not much real estate on/in my kayak...