I frequently find that trimming clay has a tendency to dry out and flake or chip over time, even when smeared with CA. A more permanent solution is self-adhesive lead tape, a product that is used to adjust the swing qualities of tennis racquets, golf clubs, etc. Since it has to stay stuck on despite the extreme impact of racquets or club heads they have a very strong adhesive. Once I know how much clay is needed on the forward or aft end of a glider, I’ll take it off and weigh it on a gram scale, then *replace it with an equal weight of lead tape. They come in a variety of widths, thicknesses, and weights (1 gram, 2 gram, etc.) and make for a nice, neat application that stays put. (You can find a huge variety on Amazon, just do a search for “lead tape”). You can still use tiny smears of clay if your glider needs re-trimming due to temperature and humidity changes. You can use nail clippers to remove bits of lead tape if need be, but I rarely have to, finding that only tiny dots of clay are needed to make adjustments. That way I can add/remove the clay whenever necessary because it’s not permanent. *It’s a good idea to do a trimming flight or two to see how your glider flies before swapping out the clay for the lead tape.