Or just have proximity detonation...
Volt, perhaps you didn't read my post.
I mention a "proximity sensor" which "would detonate if something passes fairly closely above it, or very close to the side of it."
That is basically part of the definition of proximity detonation.
All I'm saying is said proximity sensor is shaped to detect at a greater distance above it (since most players would simply try to pass over it), and when it detonates, it detonates at around head height for a standing outrider.
Proximity detonation might make more sense if mines are used (not saying I approve, though) If somebody, an HoF plants explosives on the flag, then killing the HoF who put them there makes them disappear, or go with the kamikaze method, where the death of the planter results in detonation.
An interesting concept, it would mean that new tactics would be required, however a lot of the time, mines (apart from mines at a flag, say mines sitting just inside an entrance to your base), you would want to be sitting there for a fair portion of the game, as a sort of "just in case" thing. Unless the planter remained hidden from action for the entirety of a game, I somewhat doubt that he would be able to use this tactic.