As previously stated, those "neon type" screwdrivers can send one on a wild goose chase.
It may well be a serious fault somewhere in your installation or it could be due to a broken or improper earth.
Rodents tend to chew hell out of the insulation but when it gets to the copper they usually move to the next bit of insulation, essentially leaving the conductor either partially damaged or still intact.
You may get readings on your "neon device" when the earth electrode ( if any exists) is in dry soil and the earth at the outlet is showing leakage current, the latter being normal in most instances.
Best (if you don't have already) to get an electrician in and fit either earth leakage breakers to each final sub-circuit or, as is standard practice in Thailand, fit one (as they call it) safety-cut to the main incomer.
AND..... if you must earth some piece of gear from some wild and woolly experiment, run your own earth outside to your own electrode and leave the main electrical system completely out of the loop all together.