Masking Fluid, definitely.
Easy to apply, dries quickly, easy to remove. Won't screw up the masked surface.
Automatically Appended Next Post: A masking fluid tale (true story).
I was a model painter on the movie Starship Troopers.
If you saw the movie, there's that scene where the characters are taking off from the surface of the planet and their little retrieval boat gets blasted by a tanker bug. Well, before they shot the model for that scene somebody came to the shop and asked me to do the damage on the model. I asked if it was going to need to appear undamaged again later on. I was assured that it would not be.
My boss, being a smart man, told me not to believe it. He said that I should expect to have to remove whatever it was I did to the model and put it back the way it was. With that in mind I covered the entire corner of the model with liquid latex (masking fluid) then proceeded to add all of the damage (warped bits, scorching, blue goo (which was all Citadel Blue Ink
BTW), etc.
A day or two later the guy who had asked for the damage came back in to the shop and sheepishly asked if I could put it back the way it was. I acted shocked and told him that it was probably going to take a while. I went to the set, told the
DP that he would probably want to send the guys to lunch and once everybody was gone I proceeded to tear off all of the damage in pretty much one go. There was a bit of touch-up to do but I think I had the thing pristine in about 20 minutes.
I've been a huge fan of masking fluid ever since.