Knowing what the surface of the lakes bottom is like will be very helpful when selecting a rig. Cast the marker into the area you want to check. Allow the sinker to hit the bottom then reel up the slack line till you can feel the Marker is knocking on the lead.
Now hold the rod with your fingers and not a closed hand grip. Slowly pick the rod tip up, allowing the Lead/Sinker to drag along the bottom. Through the rod feel what the sinker is doing.
If you feel the tension building and tip of the rod starts bending, then it releases and comes towards you just to get stuck again then the bottom is muddy.
You will in this case need to make a rig with longer hook links and the hook bait needs to be a Floatie or a Popup. Longer hook links will ensure that the lead does not pull your hook links and bait into the mud. Floaties or Pop Ups will sinker slower and come to rest on top of the mud or silt so the fish can get to it.
If you can feel the sinker slide easily across then it is clay. If the sinker comes towards you and you feel little knocks or bumps then you are on a gravel surface.
In order to check the Depth you will need to Make a Mark on your Rod Showing a 1Ft distance. This can be done by Measuring from the front of the Reel up the Rod 1Ft and making a Mark with some Tape or a Marker Pen.
Cast into the area you want to check. Reel up the slack line till you feel the Marker Float knock up against the Lead/Sinker. Now holding the Rod Horizontal with the ground loosen the drag or clip the Bait runner arm over. Now pinch the line between your thumb and forefinger where the line comes off the spool at the Bail Arm. Pull the line off till you reach the Marker that you have made on the rod. Count as you pull 1ft off at a time till the marker float pops out the water.
Now you Know how deep it is. Looking at the Diagram note that the depth is 9Ft at 25,5 feet away. Now you want to check if you are fishing on a Drop off. More often than not the fish like to come from deeper water and feed up the Drop off. So you want to get your lines on the Drop off. In the Diagram you will note that the Marker is on flat ground. So how do you locate the Drop off?