Frequency control at your club
Sdr,
At our club we have a similar system to yours. We have about a dozen "mini" impounds lined up along the pitts, which is about 20 or 30 yards long. Each impound has 4 frequencies on the top, and when you want to fly, you put your pin on the corresponding bolt. It also keeps all the same frequencies in one area, so pilots can keep better track of who is using the frequency.
Also try to get club members to store their pin in an obstructive place on the TX when not in use. I store mine on the left stick of my radio so I have to pin up and get it out of the way.