the two prong ones are resistive, and the exposed metal does indeed corrode quite quickly when in use. there's also a single-prong capacitive type, only very m

the two prong ones are resistive, and the exposed metal does indeed corrode quite quickly when in use. there's also a single-prong capacitive type, only very marginally more expensive, with all metal parts covered in plastic film, which can sit in the soil indefinitely.