Choosing right pump for the bore well used for irrigation purpose.

Hello everyone. We have a borewell 600 ft in depth, 6" diameter and casting with 50 feet. The near by farming companies  (floriculture companies) are using the submersible pump for lifting the water. I have seen that leakage of the gasket is a big trouble with these pump. My worry is to find out any alternative pump system if present but if the submersible pump is the only answer then how to detect the leakege of the gasket ? (or say how to reduce this problem as the pumps are very expensive). Suggetions are very much welcomed THANKS.