Let me guess, ferrets...
450kHz may propagate through the earth better than UHF, but it is going to be hard to get out a signal with a tiny antenna. The efficiency of a transmitting antenna is a function of its size relative to a half-wavelength( 1/2λ) at the operating frequency. A 1/2λ center-fed dipole antenna has a slight gain over a theoretical isotropic radiator. At 450kHz, 1/2λ = 3e8/(2χ450e3) = 333meters. I'm guessing that you want an antenna no longer than several cm, so be prepared for an antenna gain (loss) of 0.001 or worse. tens to hundreds of mW at your transmitter becomes a field strength equivalent to uW, which wont travel far in air, let alone dirt...
You would do better to use a resonant 10cm ferrite loopstick, with several hundred turns of wire on it, similar to what is used in an old transistor AM radio. That produces an h-field which might couple to a similar loop stick in your receiver. However, the orientation of the loopsticks must not be orthogonal, otherwise you get no signal. This is what the avalanche beacons do. The null is used to locate the buried skier.