What do you guys think about a way to detect enemy "seismic activity"? Basically I guess the map would just show waves where enemies are digging or throwing grenades. I suppose either some placeable seismometer with a range could be used to detect this or it could just be detected anywhere.

I know it could change the gameplay, but personally I prefer surface games over tunnel games, which feel very unpredictable to me. In reality I know it wouldn't stop tunnels from being made, but at least with this feature you could tell when the enemy breaks through some blockade you made over the tunnel.

Haha. This would be very usefull for the blue team! I kinda like your idea. But only if the detectors only can sense within a small range and are rare.