Oh, I agree, there will be nothing more effective than actually monitoring the water level in the borehole. Unfortunately it is the OP who said that this was a problem due to limited space - frankly I'm surprised that pumps of this type don't have level switches and associated protection already integrated into their housings, that's the only truly tamperproof solution (although probably a real pain if you have to pull the pump up and probably replace it if goes wrong).
Yes, reading between the lines, I think the OP is looking for an easily maintained system with minimum fault finding difficulty, maybe just a $2 meter. If the level switch is really not possible then the pressure switch could be made reasonably tamper proof - put the whole thing in a locked box with only a responsible person (who would also be held accountable for tampering). Basically Solar panel cable in, pump cable out, and the reset button inside the box too. Just a thought that even if the level sensor can be made to fit in the borehole, a pressure switch might also a good idea to prevent loss of all the water due to a broken pipe!
We can only suggest solutions at this point as the OP is the only one with actual on-the-ground knowledge of conditions.
P.S. The OP hasn't been active since 10 minutes after he posted so I doubt this is actually being read.