I've been caught by a Wallmaster twice. After the second time was when I figured out how to watch it's shadow on the ceiling and keep moving until it's shadow stopped following me. It was kinda frustrating being caught, since you had to go all the way back to the beginning of the temple.
I played the Forest Temple today and I knew, that there are Wallmasters. Navi warned me, that there are monsters on the ceiling. But I didn´t see the shadow and just stand there. Then the Wallmaster caught me and I was like "Oops" xD. The next time, I came to this room, I just jumped off the platform and killed it.