There seems to be at least two different methods of frequency control used by the majority of active clubs, the "get the pin/leave ama card", or the "cover the channel number" system.

Which system is in use at your field? What are the pro's and con's of each?

For those of you that are not familiar with the "cover your channel" system, a photo of a frequency board is shown.

The way this works is as follows. ("cover your channel")
You show up at the field with your own pin, clothes pin, or other. If you wish to fly on a particular channel, you approach the frequency board, locate your channel number, place (clip) your pin over that number, and go fly. Of course this assumes that there's no one elses pin (clip) already placed over the number.
When you're done flying, you remove your pin, and place your transmitter in the impound (hopefully you remember to turn it off).