The most consistently reliable method for me has been:
1- Dip or paint the canopy with Future Acrylic Floor Polish after trimming and polishing edges.
2- Mask with the Blue 3M low tack painter's tape, using smaller pieces to cover everything. Always use a freshly cut edge. The edges on the roll can get banged up or bent, so use a straight-edge and a sharp knife to cut pieces.
3- After masking, but before spraying the color, spray Future on the masked canopy. This will seal the edges, and any leakage will be Future, same as the canopy. After the edges are sealed, let the Future dry overnight (or at least a good while) and your paint can't run under loose edges. Works for hard edges on camoflage (never can spell that word, too lazy to look up) also, keeping paint from running under mask.
4- After decaling, sealing, weathering, and final clear coat of your choice, the mask comes off easily.
I have never had much luck with liquid masks, feeling a lack of control for the sharp edges. I used to hate masking, but a lot of that was that I worked so hard, then had to clean up the plastic after painting. Now, it comes off clean, and the shiny canopy makes it all worth while. The blue tape can also stay on longer than some other kinds without leaving residue, so modeling when I can find the time doesn't leave such a sticky mess.
PS:This is my first post, so I thought I would add an image of a favorite kit from my collection.