As stated, you would have virtually no time to react if you did see something and you would have to stare at your screen the entire time, not a good option either..
Most people boat the same waters all the time, just take your time and learn the water, ask locals about spots to avoid.
In a lake there are rarely sudden rises in the bottom so a trans mounted the conventional way will give you plenty of warning that the water is getting skinny.
On a river 1st rule is stay to the outside of a bend, almost always the deepest water and stay a good distance from islands, most of them used to be much larger than they are now, especially the front and back.
Learn to read the water, you can see things just under the surface if you know what to look for, if the water in a spot looks different than the water around it there is a reason so avoid it.
As Tommy said you could probably jury rig something up but again you would have to stare at your fish finder the entire time.