Pl Tone
A Pl tone (originally stood for "Private Line," I think a proprietary term from GE) also goes by other names including, interference eliminator and CTCSS (the most generic general term). When the radio transmits, it also sends along some bass (ie, a tone between 300 and 67 hz, there are about 20 or so to choose from). The speak on your little handheld can't reproduce this low tone, but a circuit detects it, and without it, you won't hear someone talking. So it's a way for you to avoid hearing say, the local walmart that might be grandfathered in to use a murs frequency, formerly known as "Red Dot."
If all the radios send and decode the same PL tone, you will only hear each other, unless someone else within range of you, starts sending out the same tone (not likely in the woods). Essenentially, any reasonably modern radios you get your hands one can send and receive/decode these tones. Using PL tones is a very good idea, and once they are set, you won't notice them at all.
For an example as to how they work, if you've ever used an FRS/GMRS bubble pack radio, you might notice it has two numbers, one for the channel number another for a code you can set. On some of the ones I use, channel 8, with code 13, comes out to something like 462.xxx mhz with a 127.3 hz tone, or so. Now I don't hear every kid in the neighrbood, just mine when he calls.
JB