One of the exercises Lily had been studying in the 'De Magia Unicornis' book was about establishing and maintaining a secret, low-level draw on magical power; the kind that wouldn't be externally noticeable. With the energy it would let her channel, she’d be one step closer to raising her magical barrier. Maybe it wouldn't be the sturdiest shield ever thrown up to begin with, but it would keep these cloaked Night Guard ponies from striking a first blow.