I made a spring Mine way back in the day when I first started playing Airsoft. I also made several different types of gas Mines as well. In my experience springs and gas are a waste of time. They are to complicated and take to long to set up. And just dont have the power or noise to make it worth all the time put into them. I think a Mine that just made a lot of noise would be more effective and interesting. You could just declare the person who tripped it dead and at least you got one person.
Something as simple as a trigger that drops a hammer onto a primer. Would scare the shit out of you and guarantee one kill. It would also alert everyone in the area that someone just tripped a mine and died.
After all my experimenting I honestly believe that Pyro is the only way to go. Its cheap, easy and effective. The only doubt I have is that Ive heard Madmax is working on an effective grenade that uses green gas. If anyone could figure it out I think that would be the person.
Here some pictures and a video of my Mine I built way back when. It looks effective but the spring had to be so powerful it made it a pain to set up. It would take about 150lbs to compress the spring. So if you weigh less then that you would need some help.