I was thinking something along the lines of this would be cool.
Some kind of point-defense grenade that would generate a vector tripwire after you planted two of them in a short enough radius to one another could be neat if utilized properly. Sort of like Sylux's weird snare-bomb things in Metroid Prime: Hunters.
That sort of thing is cool but I don't think it fits Halo's playstyle to have to plant two of them and worry about the distance and tripwire. Too much effort and standing around. I prefer a simple proximity trigger. Maybe still with some sort of vector effect, a red area scan that happens every 10 seconds or so to give a hint that it's there.
Wait a second, doesn't Destiny already have something like this? Whoops.
Shouldn't a map's design compliment its player count? Wouldn't a Proximity Mine act like another teammate, defending a choke point without actually putting a man on it? I'm not sure claymores or bouncing betties would work in Halo.
And a rocket launcher can kill an entire warthog of three people at once, which seems to be a lot more powerful than a normal single player. Just treat the mines like a power weapon. Keep them uncommon and in a central or symmetrical spawn point(s).
Besides, a mine is hardly as effective as an actual player with intelligence. An enemy could pop the mine with a single shot and it won't shoot back.
I'm not saying I've got all the answers about how it should work, I only thought of it a few minutes ago. I just think it would be a neat idea to experiment with.