- Location
- Rochester, NY
Sshhh...:27:...you're going to spoil the surprise. 
vlf antenna lengths are on the scale of hundreds of yards. You get about 60 feet water penetration.
Elf half wave antennas would be approximately 2,000 miles long.
A typical 36 inch handlepole will make a good half wave antenna for a 166mhz signal. You might get half an inch of water penetration if you're transmitting at least a couple watts.
Want to build a transmitter you can locate underwater? Build an acoustic one. Just a simple ping device. You can pick that signal up for miles, and it would be easy to locate.