Don't pull so hard that the wire breaks. Tie off the wire so it can't slip into the well-then abandon it. Check periodically to see if vibration has freed the sounder. Deep well turbines with oil-lubricated shafts tend to leak oil onto the water surface. As oil is lighter than water, it displaces the water level.
Oil is also a poor electrical conductor, which means it interferes with electrical contact.
A cheesecloth sack can protect the end of the sounder until it hits water. Coating the tip of the sounder with salt can increase its sensitivity when it reaches the water. This method is very accurate for measuring water levels to depths up to about 90 feet. Attach a lead weight to the end of a 100-foot steel measuring tape. Lower the tape down the well until a part of the chalked section is below water.