[kia345]

Why not take a suggestion from an outside party who doesn't know anything about Zone?

Let's look at the Combat Knife: S is a melee strike, and D is a toss. Why not work it like that?

Equipping Prox to S results in the current invisible mine. No one sees it, it blows up. But perhaps make the animation for "setting/burying" it longer, and limit how close the buries ones can be to each other without them setting each other off, to prevent invisible mine spamming.

While putting them on D is just "dropping" them. You quickly drop a visible mine, and there's no limit to how close they can be to each other.