Avoiding the bottom, and the rocks is purely visual. There are 4 different live video feeds that I can select from. One looking down, forward, aft, and one very wide angle camera at the rear (facing forward) that gets the whole sled and light boom in the frame. Depending on the viz and other conditions I will use the camera that gives the best view. But your right, in really bad viz you can easily run into things if your not paying attention. Around here (So Cal) we usually have at least 10-15’ viz when your down over a couple hundred feet, provided you have the right kind of lighting, and enough of it. In the shallows is a totally different story.
The winch is 1/4 hp and can move the camera at about 2’/second if needed, so I can move it pretty quickly and with a fast response. I also tow pretty slow and watch the depth finder for large obstacles.
All that said, I have run into rocks, and had close calls with lost nets and long line etc… Its all part of the fun =)