In shallower water, the cone of a typical transducer isn't very wide, so you have to be pretty accurate to get on a spot. Pus, if you aren't moving you are only going to get returns fom a fairly small area and even if there is something under you it will be just a line.

The best way to return to a spot is to have a marker buoy at hand and just chunk it over the side as close to your transducer as you can get it as soon as you see something. You'll be amazed the first time you get distracted for a second and realize you are 150ft from the buoy.