Problems with lowering submersible pump beyond rock gravel in a house in Bangalore, Karnataka - Do we need to put it in a casing to avoid damage?

Hi Experts,

In our agricultural field, we recently dug up a borewell and at 250 ft encountered water. However, the drilling was done till 400 Ft. Between 280-300 Ft, the foreman at drilling mentioned that 'loose rock gravel' is encountered and very good water beyond the rock gravel.

The submercible pump is currently lowered till 270 Ft only while the hard casing is put only till 100 Ft. The water output initially was good but its slowly getting depleted in force and quantity. I want to check with you expects on the following...

(1) Is there technology to lower a submersible 'safely' through and beyond the rock gravel? Ofcourse, I dont want to push it with force and not retrievable.

(2) Is there a way to put the submersible in a casing that it does not get damaged while pushing through gravel? Can a hard casing be put for the rock gravel