gajet31,
I have had some success with a flip up mount that I keep wedged completley up with a small piece of foam rubber block and out of the way unless I'm:
1. fishing a lake
2. In a river within a deep pool or long run looking for structure and depth drops.
Otherwise when running the river, I see little use for a depth/fishfinder, you're simply in too shallow of water and you need to be watching it and not the depthfinder; heck by time you see it you're already well past it.
I've drug gravel bottoms in strong current too many times to put a transducer on a trolling motor; I'd be buying one a week. I did see a guy with a transducer on a plastic pvc pipe clamped to the side of his jet rig that he could raise or lower at-will but didn't check out the design too closely; however seems like a good idea!