This would actually be a good modification for the Spike Traps, but maybe since we already have that it should be an new type of trap.
An obstacle like the spike trap, but that is invisible and invulnerable until it takes it’s first victim.
Ergo if it were a spike trap it hides invisible under ground until the first enemy walks across it and triggers it.
After that it becomes: visible and vulnerable.
This would allow us to put obstacles on the other side in the adjacent lanes. And Kings couldn’t just run past a whole mess of them with Sonic Blast and kill them all.