Protective shield and pass door+control translucence do not protect against regular trip. Fly protects against regular trip, but not weapon trip.

Protective shield is expensive mana-wise and isn't the longest lasting supplication if I recall. So, at L16, it probably won't be up all the time.

Shaman don't have the fly supplication, but fly potions are easy to get. However, many shaman, especially at lower ranks, do not have fly up unless they think they are about to fight. As a thief, you should be able to catch them off guard unless they are duergar. Of course, if you try to trip and they are flying, you do not attack or come out of hidden. So, keep trying every tick until you get them.