Your opponent doesn't know where your traps are. Only you can see the little "teeth" around them.
When your opponent casts a trap, you only see is a big question mark for a second every time there are new traps set.
I don't think they will ever buff shadow of the path by activating more traps ore add them to random colors. Self-Healing is just kind of the opposite of how black works and therefore it's rare and inefficient.