Actually LoRa uses chirps designed for iiuc partially analog demodulation to be very energy-efficient.

For hiding you'd be able to use actual DSSS with e.g. AES encrypting a suitably fine grained clock piggybacking on GPS as a time reference, keyed by a shared secret. Then just hone in with e.g. a Costas loop like a GPS receiver does to it's satellites (where the sequence is sourced from a simple clocked logic circuit that's cheap and offers better than random spreading gain at the cost of being cryptographically useless) and demodulate the payload the same way.

You could start off at GPS synchronous sequence generator timing, and slowly shift it at increasing delay until lock in is archived or an implausibly long implied travel distance (signal loss!) is reached (then you can give up and start over, go to sleep and try later, etc.).